[widget] Change RegisterDragDrop to be called on idle.

This is a low-priority init function that should not be called with
immediate dispatch to the current thread, for performance reasons.
Additionally, do not call RegisterDragDrop for hidden windows.

4 files changed, 17 insertions, 6 deletions

diff --git a/widget/nsBaseWidget.cpp b/widget/nsBaseWidget.cpp
index d3cdf72cfc..c72f0364bc 100644
--- a/widget/nsBaseWidget.cpp
+++ b/widget/nsBaseWidget.cpp
@@ -2133,6 +2133,16 @@ nsBaseWidget::UpdateSynthesizedTouchState(MultiTouchInput* aState,
   return inputToDispatch;
 }
 
+nsresult
+nsBaseWidget::AsyncEnableDragDrop(bool aEnable)
+{
+  RefPtr<nsBaseWidget> kungFuDeathGrip = this;
+  return NS_IdleDispatchToCurrentThread(
+    NS_NewRunnableFunction([this, aEnable, kungFuDeathGrip]() {
+                             EnableDragDrop(aEnable);
+                           }));
+}
+
 void
 nsBaseWidget::RegisterPluginWindowForRemoteUpdates()
 {
diff --git a/widget/nsBaseWidget.h b/widget/nsBaseWidget.h
index bbc6b72383..ab29fcd0ff 100644
--- a/widget/nsBaseWidget.h
+++ b/widget/nsBaseWidget.h
@@ -243,6 +243,7 @@ public:
   NS_IMETHOD              SetNonClientMargins(LayoutDeviceIntMargin& aMargins) override;
   virtual LayoutDeviceIntPoint GetClientOffset() override;
   virtual void            EnableDragDrop(bool aEnable) override {};
+  virtual nsresult        AsyncEnableDragDrop(bool aEnable) override;
   NS_IMETHOD              GetAttention(int32_t aCycleCount) override;
   virtual bool            HasPendingInputEvent() override;
   NS_IMETHOD              SetIcon(const nsAString &anIconSpec) override;
diff --git a/widget/nsIWidget.h b/widget/nsIWidget.h
index 8e28c24da5..fe21b67275 100644
--- a/widget/nsIWidget.h
+++ b/widget/nsIWidget.h
@@ -1378,6 +1378,7 @@ class nsIWidget : public nsISupports
      * Enables the dropping of files to a widget.
      */
     virtual void EnableDragDrop(bool aEnable) = 0;
+    virtual nsresult AsyncEnableDragDrop(bool aEnable) = 0;
 
     /**
      * Enables/Disables system mouse capture.
diff --git a/widget/windows/nsWindow.cpp b/widget/windows/nsWindow.cpp
index 8f614d8628..295518ea26 100644
--- a/widget/windows/nsWindow.cpp
+++ b/widget/windows/nsWindow.cpp
@@ -3715,22 +3715,21 @@ nsWindow::ClientToWindowSize(const LayoutDeviceIntSize& aClientSize)
 void
 nsWindow::EnableDragDrop(bool aEnable)
 {
-  NS_ASSERTION(mWnd, "nsWindow::EnableDragDrop() called after Destroy()");
+  if (!mWnd) {
+    // Return early if the window already closed
+    return;
+  }
 
   nsresult rv = NS_ERROR_FAILURE;
   if (aEnable) {
     if (!mNativeDragTarget) {
       mNativeDragTarget = new nsNativeDragTarget(this);
       mNativeDragTarget->AddRef();
-      if (SUCCEEDED(::CoLockObjectExternal((LPUNKNOWN)mNativeDragTarget,
-                                           TRUE, FALSE))) {
-        ::RegisterDragDrop(mWnd, (LPDROPTARGET)mNativeDragTarget);
-      }
+      ::RegisterDragDrop(mWnd, (LPDROPTARGET)mNativeDragTarget);
     }
   } else {
     if (mWnd && mNativeDragTarget) {
       ::RevokeDragDrop(mWnd);
-      ::CoLockObjectExternal((LPUNKNOWN)mNativeDragTarget, FALSE, TRUE);
       mNativeDragTarget->DragCancel();
       NS_RELEASE(mNativeDragTarget);
     }