path: root/dom/plugins/ipc/PluginInstanceChild.h

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: sw=4 ts=4 et :
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef dom_plugins_PluginInstanceChild_h
#define dom_plugins_PluginInstanceChild_h 1

#include "mozilla/EventForwards.h"
#include "mozilla/plugins/PPluginInstanceChild.h"
#include "mozilla/plugins/PluginScriptableObjectChild.h"
#include "mozilla/plugins/StreamNotifyChild.h"
#include "mozilla/plugins/PPluginSurfaceChild.h"
#include "mozilla/ipc/CrossProcessMutex.h"
#include "nsRefPtrHashtable.h"
#if defined(OS_WIN)
#include "mozilla/gfx/SharedDIBWin.h"
#elif defined(MOZ_WIDGET_COCOA)
#include "PluginUtilsOSX.h"
#include "mozilla/gfx/QuartzSupport.h"
#include "base/timer.h"

#endif

#include "npfunctions.h"
#include "nsAutoPtr.h"
#include "nsTArray.h"
#include "ChildAsyncCall.h"
#include "ChildTimer.h"
#include "nsRect.h"
#include "nsTHashtable.h"
#include "mozilla/PaintTracker.h"
#include "mozilla/gfx/Types.h"

#include <map>

#ifdef MOZ_WIDGET_GTK
#include "gtk2xtbin.h"
#endif

class gfxASurface;

namespace mozilla {
namespace plugins {

class PBrowserStreamChild;
class BrowserStreamChild;
class StreamNotifyChild;

class PluginInstanceChild : public PPluginInstanceChild
{
    friend class BrowserStreamChild;
    friend class PluginStreamChild;
    friend class StreamNotifyChild;
    friend class PluginScriptableObjectChild;

#ifdef OS_WIN
    friend LRESULT CALLBACK PluginWindowProc(HWND hWnd,
                                             UINT message,
                                             WPARAM wParam,
                                             LPARAM lParam);
    static LRESULT CALLBACK PluginWindowProcInternal(HWND hWnd,
                                                     UINT message,
                                                     WPARAM wParam,
                                                     LPARAM lParam);
#endif

protected:
    virtual bool
    AnswerCreateChildPluginWindow(NativeWindowHandle* aChildPluginWindow) override;

    virtual bool
    RecvCreateChildPopupSurrogate(const NativeWindowHandle& aNetscapeWindow) override;

    virtual bool
    AnswerNPP_SetWindow(const NPRemoteWindow& window) override;

    virtual bool
    AnswerNPP_GetValue_NPPVpluginWantsAllNetworkStreams(bool* wantsAllStreams, NPError* rv) override;
    virtual bool
    AnswerNPP_GetValue_NPPVpluginNeedsXEmbed(bool* needs, NPError* rv) override;
    virtual bool
    AnswerNPP_GetValue_NPPVpluginScriptableNPObject(PPluginScriptableObjectChild** value,
                                                    NPError* result) override;
    virtual bool
    AnswerNPP_GetValue_NPPVpluginNativeAccessibleAtkPlugId(nsCString* aPlugId,
                                                           NPError* aResult) override;
    virtual bool
    AnswerNPP_SetValue_NPNVprivateModeBool(const bool& value, NPError* result) override;
    virtual bool
    AnswerNPP_SetValue_NPNVmuteAudioBool(const bool& value, NPError* result) override;
    virtual bool
    AnswerNPP_SetValue_NPNVCSSZoomFactor(const double& value, NPError* result) override;

    virtual bool
    AnswerNPP_HandleEvent(const NPRemoteEvent& event, int16_t* handled) override;
    virtual bool
    AnswerNPP_HandleEvent_Shmem(const NPRemoteEvent& event,
                                Shmem&& mem,
                                int16_t* handled,
                                Shmem* rtnmem) override;
    virtual bool
    AnswerNPP_HandleEvent_IOSurface(const NPRemoteEvent& event,
                                    const uint32_t& surface,
                                    int16_t* handled) override;

    // Async rendering
    virtual bool
    RecvAsyncSetWindow(const gfxSurfaceType& aSurfaceType,
                       const NPRemoteWindow& aWindow) override;

    virtual void
    DoAsyncSetWindow(const gfxSurfaceType& aSurfaceType,
                     const NPRemoteWindow& aWindow,
                     bool aIsAsync);

    virtual PPluginSurfaceChild*
    AllocPPluginSurfaceChild(const WindowsSharedMemoryHandle&,
                             const gfx::IntSize&, const bool&) override {
        return new PPluginSurfaceChild();
    }

    virtual bool DeallocPPluginSurfaceChild(PPluginSurfaceChild* s) override {
        delete s;
        return true;
    }

    virtual bool
    AnswerPaint(const NPRemoteEvent& event, int16_t* handled) override
    {
        PaintTracker pt;
        return AnswerNPP_HandleEvent(event, handled);
    }

    virtual bool
    RecvWindowPosChanged(const NPRemoteEvent& event) override;

    virtual bool
    RecvContentsScaleFactorChanged(const double& aContentsScaleFactor) override;

    virtual bool
    AnswerNPP_Destroy(NPError* result) override;

    virtual PPluginScriptableObjectChild*
    AllocPPluginScriptableObjectChild() override;

    virtual bool
    DeallocPPluginScriptableObjectChild(PPluginScriptableObjectChild* aObject) override;

    virtual bool
    RecvPPluginScriptableObjectConstructor(PPluginScriptableObjectChild* aActor) override;

    virtual bool
    RecvPBrowserStreamConstructor(PBrowserStreamChild* aActor, const nsCString& aURL,
                                  const uint32_t& aLength, const uint32_t& aLastmodified,
                                  PStreamNotifyChild* aNotifyData, const nsCString& aHeaders) override;

    virtual bool
    AnswerNPP_NewStream(
            PBrowserStreamChild* actor,
            const nsCString& mimeType,
            const bool& seekable,
            NPError* rv,
            uint16_t* stype) override;

    virtual bool
    RecvAsyncNPP_NewStream(
            PBrowserStreamChild* actor,
            const nsCString& mimeType,
            const bool& seekable) override;

    virtual PBrowserStreamChild*
    AllocPBrowserStreamChild(const nsCString& url,
                             const uint32_t& length,
                             const uint32_t& lastmodified,
                             PStreamNotifyChild* notifyData,
                             const nsCString& headers) override;

    virtual bool
    DeallocPBrowserStreamChild(PBrowserStreamChild* stream) override;

    virtual PPluginStreamChild*
    AllocPPluginStreamChild(const nsCString& mimeType,
                            const nsCString& target,
                            NPError* result) override;

    virtual bool
    DeallocPPluginStreamChild(PPluginStreamChild* stream) override;

    virtual PStreamNotifyChild*
    AllocPStreamNotifyChild(const nsCString& url, const nsCString& target,
                            const bool& post, const nsCString& buffer,
                            const bool& file,
                            NPError* result) override;

    virtual bool
    DeallocPStreamNotifyChild(PStreamNotifyChild* notifyData) override;

    virtual bool
    AnswerSetPluginFocus() override;

    virtual bool
    AnswerUpdateWindow() override;

    virtual bool
    RecvNPP_DidComposite() override;

#if defined(MOZ_X11) && defined(XP_UNIX)
    bool CreateWindow(const NPRemoteWindow& aWindow);
    void DeleteWindow();
#endif

public:
    PluginInstanceChild(const NPPluginFuncs* aPluginIface,
                        const nsCString& aMimeType,
                        const uint16_t& aMode,
                        const InfallibleTArray<nsCString>& aNames,
                        const InfallibleTArray<nsCString>& aValues);

    virtual ~PluginInstanceChild();

    NPError DoNPP_New();

    // Common sync+async implementation of NPP_NewStream
    NPError DoNPP_NewStream(BrowserStreamChild* actor,
                            const nsCString& mimeType,
                            const bool& seekable,
                            uint16_t* stype);

    bool Initialize();

    NPP GetNPP()
    {
        return &mData;
    }

    NPError
    NPN_GetValue(NPNVariable aVariable, void* aValue);

    NPError
    NPN_SetValue(NPPVariable aVariable, void* aValue);

    PluginScriptableObjectChild*
    GetActorForNPObject(NPObject* aObject);

    NPError
    NPN_NewStream(NPMIMEType aMIMEType, const char* aWindow,
                  NPStream** aStream);

    void InvalidateRect(NPRect* aInvalidRect);

#ifdef MOZ_WIDGET_COCOA
    void Invalidate();
#endif // definied(MOZ_WIDGET_COCOA)

    uint32_t ScheduleTimer(uint32_t interval, bool repeat, TimerFunc func);
    void UnscheduleTimer(uint32_t id);

    void AsyncCall(PluginThreadCallback aFunc, void* aUserData);
    // This function is a more general version of AsyncCall
    void PostChildAsyncCall(already_AddRefed<ChildAsyncCall> aTask);

    int GetQuirks();

    void NPN_URLRedirectResponse(void* notifyData, NPBool allow);


    NPError NPN_InitAsyncSurface(NPSize *size, NPImageFormat format,
                                 void *initData, NPAsyncSurface *surface);
    NPError NPN_FinalizeAsyncSurface(NPAsyncSurface *surface);

    void NPN_SetCurrentAsyncSurface(NPAsyncSurface *surface, NPRect *changed);

    void DoAsyncRedraw();

    virtual bool RecvHandledWindowedPluginKeyEvent(
                   const NativeEventData& aKeyEventData,
                   const bool& aIsConsumed) override;

#if defined(XP_WIN)
    NPError DefaultAudioDeviceChanged(NPAudioDeviceChangeDetails& details);
#endif

private:
    friend class PluginModuleChild;

    NPError
    InternalGetNPObjectForValue(NPNVariable aValue,
                                NPObject** aObject);

    bool IsUsingDirectDrawing();

    virtual bool RecvUpdateBackground(const SurfaceDescriptor& aBackground,
                                      const nsIntRect& aRect) override;

    virtual PPluginBackgroundDestroyerChild*
    AllocPPluginBackgroundDestroyerChild() override;

    virtual bool
    RecvPPluginBackgroundDestroyerConstructor(PPluginBackgroundDestroyerChild* aActor) override;

    virtual bool
    DeallocPPluginBackgroundDestroyerChild(PPluginBackgroundDestroyerChild* aActor) override;

#if defined(OS_WIN)
    static bool RegisterWindowClass();
    bool CreatePluginWindow();
    void DestroyPluginWindow();
    void SizePluginWindow(int width, int height);
    int16_t WinlessHandleEvent(NPEvent& event);
    void CreateWinlessPopupSurrogate();
    void DestroyWinlessPopupSurrogate();
    void InitPopupMenuHook();
    void SetupFlashMsgThrottle();
    void UnhookWinlessFlashThrottle();
    void HookSetWindowLongPtr();
    void SetUnityHooks();
    void ClearUnityHooks();
    void InitImm32Hook();
    static inline bool SetWindowLongHookCheck(HWND hWnd,
                                                int nIndex,
                                                LONG_PTR newLong);
    void FlashThrottleMessage(HWND, UINT, WPARAM, LPARAM, bool);
    static LRESULT CALLBACK DummyWindowProc(HWND hWnd,
                                            UINT message,
                                            WPARAM wParam,
                                            LPARAM lParam);
    static LRESULT CALLBACK PluginWindowProc(HWND hWnd,
                                             UINT message,
                                             WPARAM wParam,
                                             LPARAM lParam);
    static BOOL WINAPI TrackPopupHookProc(HMENU hMenu,
                                          UINT uFlags,
                                          int x,
                                          int y,
                                          int nReserved,
                                          HWND hWnd,
                                          CONST RECT *prcRect);
    static HWND WINAPI SetCaptureHook(HWND aHwnd);
    static LRESULT CALLBACK UnityGetMessageHookProc(int aCode, WPARAM aWparam, LPARAM aLParam);
    static LRESULT CALLBACK UnitySendMessageHookProc(int aCode, WPARAM aWparam, LPARAM aLParam);
    static BOOL CALLBACK EnumThreadWindowsCallback(HWND hWnd,
                                                   LPARAM aParam);
    static LRESULT CALLBACK WinlessHiddenFlashWndProc(HWND hWnd,
                                                      UINT message,
                                                      WPARAM wParam,
                                                      LPARAM lParam);
#ifdef _WIN64
    static LONG_PTR WINAPI SetWindowLongPtrAHook(HWND hWnd,
                                                 int nIndex,
                                                 LONG_PTR newLong);
    static LONG_PTR WINAPI SetWindowLongPtrWHook(HWND hWnd,
                                                 int nIndex,
                                                 LONG_PTR newLong);
                      
#else
    static LONG WINAPI SetWindowLongAHook(HWND hWnd,
                                          int nIndex,
                                          LONG newLong);
    static LONG WINAPI SetWindowLongWHook(HWND hWnd,
                                          int nIndex,
                                          LONG newLong);
#endif

    static HIMC WINAPI ImmGetContextProc(HWND aWND);
    static BOOL WINAPI ImmReleaseContextProc(HWND aWND, HIMC aIMC);
    static LONG WINAPI ImmGetCompositionStringProc(HIMC aIMC, DWORD aIndex,
                                                   LPVOID aBuf, DWORD aLen);
    static BOOL WINAPI ImmSetCandidateWindowProc(HIMC hIMC,
                                                 LPCANDIDATEFORM plCandidate);
    static BOOL WINAPI ImmNotifyIME(HIMC aIMC, DWORD aAction, DWORD aIndex,
                                    DWORD aValue);

    class FlashThrottleAsyncMsg : public ChildAsyncCall
    {
      public:
        FlashThrottleAsyncMsg();
        FlashThrottleAsyncMsg(PluginInstanceChild* aInst, 
                              HWND aWnd, UINT aMsg,
                              WPARAM aWParam, LPARAM aLParam,
                              bool isWindowed)
          : ChildAsyncCall(aInst, nullptr, nullptr),
          mWnd(aWnd),
          mMsg(aMsg),
          mWParam(aWParam),
          mLParam(aLParam),
          mWindowed(isWindowed)
        {}

        NS_IMETHOD Run() override;

        WNDPROC GetProc();
        HWND GetWnd() { return mWnd; }
        UINT GetMsg() { return mMsg; }
        WPARAM GetWParam() { return mWParam; }
        LPARAM GetLParam() { return mLParam; }

      private:
        HWND                 mWnd;
        UINT                 mMsg;
        WPARAM               mWParam;
        LPARAM               mLParam;
        bool                 mWindowed;
    };

    bool ShouldPostKeyMessage(UINT message, WPARAM wParam, LPARAM lParam);
    bool MaybePostKeyMessage(UINT message, WPARAM wParam, LPARAM lParam);
#endif // #if defined(OS_WIN)
    const NPPluginFuncs* mPluginIface;
    nsCString                   mMimeType;
    uint16_t                    mMode;
    InfallibleTArray<nsCString> mNames;
    InfallibleTArray<nsCString> mValues;
    NPP_t mData;
    NPWindow mWindow;
#if defined(XP_WIN)
    double mContentsScaleFactor;
#endif
    double mCSSZoomFactor;
    uint32_t mPostingKeyEvents;
    uint32_t mPostingKeyEventsOutdated;
    int16_t               mDrawingModel;

    NPAsyncSurface* mCurrentDirectSurface;

    // The surface hashtables below serve a few purposes. They let us verify
    // and retain extra information about plugin surfaces, and they let us
    // free shared memory that the plugin might forget to release.
    struct DirectBitmap {
        DirectBitmap(PluginInstanceChild* aOwner, const Shmem& shmem,
                     const gfx::IntSize& size, uint32_t stride, SurfaceFormat format);

      private:
        ~DirectBitmap();

      public:
        NS_INLINE_DECL_THREADSAFE_REFCOUNTING(DirectBitmap);

        PluginInstanceChild* mOwner;
        Shmem mShmem;
        gfx::SurfaceFormat mFormat;
        gfx::IntSize mSize;
        uint32_t mStride;
    };
    nsRefPtrHashtable<nsPtrHashKey<NPAsyncSurface>, DirectBitmap> mDirectBitmaps;

#if defined(XP_WIN)
    nsDataHashtable<nsPtrHashKey<NPAsyncSurface>, WindowsHandle> mDxgiSurfaces;
#endif

    mozilla::Mutex mAsyncInvalidateMutex;
    CancelableRunnable *mAsyncInvalidateTask;

    // Cached scriptable actors to avoid IPC churn
    PluginScriptableObjectChild* mCachedWindowActor;
    PluginScriptableObjectChild* mCachedElementActor;

#if defined(MOZ_X11) && defined(XP_UNIX)
    NPSetWindowCallbackStruct mWsInfo;
#ifdef MOZ_WIDGET_GTK
    bool mXEmbed;
    XtClient mXtClient;
#endif
#elif defined(OS_WIN)
    HWND mPluginWindowHWND;
    WNDPROC mPluginWndProc;
    HWND mPluginParentHWND;
    int mNestedEventLevelDepth;
    HWND mCachedWinlessPluginHWND;
    HWND mWinlessPopupSurrogateHWND;
    nsIntPoint mPluginSize;
    WNDPROC mWinlessThrottleOldWndProc;
    HWND mWinlessHiddenMsgHWND;
    HHOOK mUnityGetMessageHook;
    HHOOK mUnitySendMessageHook;
#endif

    friend class ChildAsyncCall;

    Mutex mAsyncCallMutex;
    nsTArray<ChildAsyncCall*> mPendingAsyncCalls;
    nsTArray<nsAutoPtr<ChildTimer> > mTimers;

    /**
     * During destruction we enumerate all remaining scriptable objects and
     * invalidate/delete them. Enumeration can re-enter, so maintain a
     * hash separate from PluginModuleChild.mObjectMap.
     */
    nsAutoPtr< nsTHashtable<DeletingObjectEntry> > mDeletingHash;

#if defined(MOZ_WIDGET_COCOA)
private:
#if defined(__i386__)
    NPEventModel                  mEventModel;
#endif
    CGColorSpaceRef               mShColorSpace;
    CGContextRef                  mShContext;
    RefPtr<nsCARenderer> mCARenderer;
    void                         *mCGLayer;

    // Core Animation drawing model requires a refresh timer.
    uint32_t                      mCARefreshTimer;

public:
    const NPCocoaEvent* getCurrentEvent() {
        return mCurrentEvent;
    }
  
    bool CGDraw(CGContextRef ref, nsIntRect aUpdateRect);

#if defined(__i386__)
    NPEventModel EventModel() { return mEventModel; }
#endif

private:
    const NPCocoaEvent   *mCurrentEvent;
#endif

    bool CanPaintOnBackground();

    bool IsVisible() {
        return mWindow.clipRect.top != 0 ||
            mWindow.clipRect.left != 0 ||
            mWindow.clipRect.bottom != 0 ||
            mWindow.clipRect.right != 0;
    }

    // ShowPluginFrame - in general does four things:
    // 1) Create mCurrentSurface optimized for rendering to parent process
    // 2) Updated mCurrentSurface to be a complete copy of mBackSurface
    // 3) Draw the invalidated plugin area into mCurrentSurface
    // 4) Send it to parent process.
    bool ShowPluginFrame(void);

    // If we can read back safely from mBackSurface, copy
    // mSurfaceDifferenceRect from mBackSurface to mFrontSurface.
    // @return Whether the back surface could be read.
    bool ReadbackDifferenceRect(const nsIntRect& rect);

    // Post ShowPluginFrame task
    void AsyncShowPluginFrame(void);

    // In the PaintRect functions, aSurface is the size of the full plugin
    // window. Each PaintRect function renders into the subrectangle aRect of
    // aSurface (possibly more if we're working around a Flash bug).

    // Paint plugin content rectangle to surface with bg color filling
    void PaintRectToSurface(const nsIntRect& aRect,
                            gfxASurface* aSurface,
                            const gfx::Color& aColor);

    // Render plugin content to surface using
    // white/black image alpha extraction algorithm
    void PaintRectWithAlphaExtraction(const nsIntRect& aRect,
                                      gfxASurface* aSurface);

    // Call plugin NPAPI function to render plugin content to surface
    // @param - aSurface - should be compatible with current platform plugin rendering
    // @return - FALSE if plugin not painted to surface
    void PaintRectToPlatformSurface(const nsIntRect& aRect,
                                    gfxASurface* aSurface);

    // Update NPWindow platform attributes and call plugin "setwindow"
    // @param - aForceSetWindow - call setwindow even if platform attributes are the same
    void UpdateWindowAttributes(bool aForceSetWindow = false);

    // Create optimized mCurrentSurface for parent process rendering
    // @return FALSE if optimized surface not created
    bool CreateOptSurface(void);

    // Create mHelperSurface if mCurrentSurface non compatible with plugins
    // @return TRUE if helper surface created successfully, or not needed
    bool MaybeCreatePlatformHelperSurface(void);

    // Make sure that we have surface for rendering
    bool EnsureCurrentBuffer(void);

    // Helper function for delayed InvalidateRect call
    // non null mCurrentInvalidateTask will call this function
    void InvalidateRectDelayed(void);

    // Clear mCurrentSurface/mCurrentSurfaceActor/mHelperSurface
    void ClearCurrentSurface();

    // Swap mCurrentSurface/mBackSurface and their associated actors
    void SwapSurfaces();

    // Clear all surfaces in response to NPP_Destroy
    void ClearAllSurfaces();

    void Destroy();

    void ActorDestroy(ActorDestroyReason aWhy) override;

    // Set as true when SetupLayer called
    // and go with different path in InvalidateRect function
    bool mLayersRendering;

    // Current surface available for rendering
    RefPtr<gfxASurface> mCurrentSurface;

    // Back surface, just keeping reference to
    // surface which is on ParentProcess side
    RefPtr<gfxASurface> mBackSurface;

    // (Not to be confused with mBackSurface).  This is a recent copy
    // of the opaque pixels under our object frame, if
    // |mIsTransparent|.  We ask the plugin render directly onto a
    // copy of the background pixels if available, and fall back on
    // alpha recovery otherwise.
    RefPtr<gfxASurface> mBackground;

#ifdef XP_WIN
    // These actors mirror mCurrentSurface/mBackSurface
    PPluginSurfaceChild* mCurrentSurfaceActor;
    PPluginSurfaceChild* mBackSurfaceActor;
#endif

    // Accumulated invalidate rect, while back buffer is not accessible,
    // in plugin coordinates.
    nsIntRect mAccumulatedInvalidRect;

    // Plugin only call SetTransparent
    // and does not remember their transparent state
    // and p->getvalue return always false
    bool mIsTransparent;

    // Surface type optimized of parent process
    gfxSurfaceType mSurfaceType;

    // Keep InvalidateRect task pointer to be able Cancel it on Destroy
    RefPtr<CancelableRunnable> mCurrentInvalidateTask;

    // Keep AsyncSetWindow task pointer to be able to Cancel it on Destroy
    RefPtr<CancelableRunnable> mCurrentAsyncSetWindowTask;

    // True while plugin-child in plugin call
    // Use to prevent plugin paint re-enter
    bool mPendingPluginCall;

    // On some platforms, plugins may not support rendering to a surface with
    // alpha, or not support rendering to an image surface.
    // In those cases we need to draw to a temporary platform surface; we cache
    // that surface here.
    RefPtr<gfxASurface> mHelperSurface;

    // true when plugin does not support painting to ARGB32
    // surface this is false if plugin supports
    // NPPVpluginTransparentAlphaBool (which is not part of
    // NPAPI yet)
    bool mDoAlphaExtraction;

    // true when the plugin has painted at least once. We use this to ensure
    // that we ask a plugin to paint at least once even if it's invisible;
    // some plugin (instances) rely on this in order to work properly.
    bool mHasPainted;

    // Cached rectangle rendered to previous surface(mBackSurface)
    // Used for reading back to current surface and syncing data,
    // in plugin coordinates.
    nsIntRect mSurfaceDifferenceRect;

    // Has this instance been destroyed, either by ActorDestroy or NPP_Destroy?
    bool mDestroyed;

#ifdef XP_WIN
    // WM_*CHAR messages are never consumed by chrome process's widget.
    // So, if preceding keydown or keyup event is consumed by reserved
    // shortcut key in the chrome process, we shouldn't send the following
    // WM_*CHAR messages to the plugin.
    bool mLastKeyEventConsumed;
#endif // #ifdef XP_WIN

    // While IME in the process has composition, this is set to true.
    // Otherwise, false.
    static bool sIsIMEComposing;

    // A counter is incremented by AutoStackHelper to indicate that there is an
    // active plugin call which should be preventing shutdown.
public:
    class AutoStackHelper {
    public:
        explicit AutoStackHelper(PluginInstanceChild* instance)
            : mInstance(instance)
        {
            ++mInstance->mStackDepth;
        }
        ~AutoStackHelper() {
            --mInstance->mStackDepth;
        }
    private:
        PluginInstanceChild *const mInstance;
    };
private:
    int32_t mStackDepth;
};

} // namespace plugins
} // namespace mozilla

#endif // ifndef dom_plugins_PluginInstanceChild_h