Bug 1343937 - Fix a crash in nsWrapperCache.h

* Implement and use GetInFlowParent
* Exempt scrollbar NAC from the new NAC semantics

Tag mcp-graveyard/UXP#1375

3 files changed, 22 insertions, 2 deletions

diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index 2b81ce83b9..71f6172bd5 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -8964,10 +8964,10 @@ GetCorrectedParent(const nsIFrame* aFrame)
   nsIContent* content = aFrame->GetContent();
   Element* element =
     content && content->IsElement() ? content->AsElement() : nullptr;
-  if (element && element->IsNativeAnonymous() &&
+  if (element && element->IsNativeAnonymous() && !element->IsNativeScrollbarContent() &&
       element->GetPseudoElementType() == aFrame->StyleContext()->GetPseudoType()) {
     while (parent->GetContent() && parent->GetContent()->IsNativeAnonymous()) {
-      parent = parent->GetParent();
+      parent = parent->GetInFlowParent();
     }
   }
 
diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
index 93eb95099a..3137aaee27 100644
--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -721,6 +721,13 @@ public:
    * Accessor functions for geometric parent.
    */
   nsContainerFrame* GetParent() const { return mParent; }
+
+  /**
+   * Gets the parent of a frame, using the parent of the placeholder for
+   * out-of-flow frames.
+   */
+  inline nsContainerFrame* GetInFlowParent();
+
   /**
    * Set this frame's parent to aParent.
    * If the frame may have moved into or out of a scrollframe's
diff --git a/layout/generic/nsIFrameInlines.h b/layout/generic/nsIFrameInlines.h
index eb9a7202a3..3068c9f79d 100644
--- a/layout/generic/nsIFrameInlines.h
+++ b/layout/generic/nsIFrameInlines.h
@@ -8,8 +8,10 @@
 #define nsIFrameInlines_h___
 
 #include "nsContainerFrame.h"
+#include "nsPlaceholderFrame.h"
 #include "nsStyleStructInlines.h"
 #include "nsCSSAnonBoxes.h"
+#include "nsFrameManager.h"
 
 bool
 nsIFrame::IsFlexItem() const
@@ -160,4 +162,15 @@ nsIFrame::BaselineBOffset(mozilla::WritingMode aWM,
   return SynthesizeBaselineBOffsetFromBorderBox(aWM, aBaselineGroup);
 }
 
+nsContainerFrame*
+nsIFrame::GetInFlowParent()
+{
+  if (GetStateBits() & NS_FRAME_OUT_OF_FLOW) {
+    nsFrameManager* fm = PresContext()->FrameManager();
+    return fm->GetPlaceholderFrameFor(FirstContinuation())->GetParent();
+  }
+
+  return GetParent();
+}
+
 #endif