Bug 1363922 - Part 1: Remember about the reference frame during BuildDisplayList for ScrollFrameHelper so GetScrolledRect can use it. r=mstange

MozReview-Commit-ID: 8GO6xuSH5xY

layout/base/nsLayoutUtils.h

@@ -3134,4 +3134,21 @@ public:
   nsCOMPtr<nsIAtom> mAttrName;
 };
 
+// This class allows you to easily set any pointer variable and ensure it's
+// set to nullptr when leaving its scope.
+template<typename T>
+class MOZ_RAII SetAndNullOnExit
+{
+public:
+  SetAndNullOnExit(T* &aVariable, T* aValue) {
+    aVariable = aValue;
+    mVariable = &aVariable;
+  }
+  ~SetAndNullOnExit() {
+    *mVariable = nullptr;
+  }
+private:
+  T** mVariable;
+};
+
 #endif // nsLayoutUtils_h__

layout/generic/nsGfxScrollFrame.cpp

@@ -2006,6 +2006,7 @@ ScrollFrameHelper::ScrollFrameHelper(nsContainerFrame* aOuter,
   , mScrollCornerBox(nullptr)
   , mResizerBox(nullptr)
   , mOuter(aOuter)
+  , mReferenceFrameDuringPainting(nullptr)
   , mAsyncScroll(nullptr)
   , mAsyncSmoothMSDScroll(nullptr)
   , mLastScrollOrigin(nsGkAtoms::other)
@@ -3263,6 +3264,7 @@ void
 ScrollFrameHelper::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
                                     const nsDisplayListSet& aLists)
 {
+  SetAndNullOnExit<const nsIFrame> tmpBuilder(mReferenceFrameDuringPainting, aBuilder->GetCurrentReferenceFrame());
   if (aBuilder->IsForFrameVisibility()) {
     NotifyApproximateFrameVisibilityUpdate(false);
   }
@@ -5866,7 +5868,8 @@ ScrollFrameHelper::GetScrolledRect() const
   // relative to the reference frame, since that's the space where painting does
   // snapping.
   nsSize scrollPortSize = GetScrollPositionClampingScrollPortSize();
-  nsIFrame* referenceFrame = nsLayoutUtils::GetReferenceFrame(mOuter);
+  const nsIFrame* referenceFrame =
+    mReferenceFrameDuringPainting ? mReferenceFrameDuringPainting : nsLayoutUtils::GetReferenceFrame(mOuter);
   nsPoint toReferenceFrame = mOuter->GetOffsetToCrossDoc(referenceFrame);
   nsRect scrollPort(mScrollPort.TopLeft() + toReferenceFrame, scrollPortSize);
   nsRect scrolledRect = result + scrollPort.TopLeft();

layout/generic/nsGfxScrollFrame.h

@@ -493,6 +493,7 @@ public:
   nsIFrame* mScrollCornerBox;
   nsIFrame* mResizerBox;
   nsContainerFrame* mOuter;
+  const nsIFrame* mReferenceFrameDuringPainting;
   RefPtr<AsyncScroll> mAsyncScroll;
   RefPtr<AsyncSmoothMSDScroll> mAsyncSmoothMSDScroll;
   RefPtr<ScrollbarActivity> mScrollbarActivity;