Bug 1178745 - Add an nsIScrollableFrame API for getting the scroll clip. r=roc

--HG--
extra : rebase_source : 8f2b62b0ce23dcfece6984d89a774a96453ecb6e
extra : histedit_source : 586e99a17ecbb86dc243568cee1ebf1d24f37717

layout/generic/nsGfxScrollFrame.cpp

@@ -3089,6 +3089,17 @@ ScrollFrameHelper::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
   scrolledContent.MoveTo(aLists);
 }
 
+const DisplayItemClip*
+ScrollFrameHelper::ComputeScrollClip(bool aIsForCaret) const
+{
+  const DisplayItemClip* ancestorClip = aIsForCaret ? mAncestorClipForCaret : mAncestorClip;
+  if (!mShouldBuildScrollableLayer || mIsScrollableLayerInRootContainer) {
+    return nullptr;
+  }
+
+  return ancestorClip;
+}
+
 Maybe<FrameMetricsAndClip>
 ScrollFrameHelper::ComputeFrameMetrics(Layer* aLayer,
                                        nsIFrame* aContainerReferenceFrame,

layout/generic/nsGfxScrollFrame.h

@@ -381,6 +381,7 @@ public:
     Layer* aLayer, nsIFrame* aContainerReferenceFrame,
     const ContainerLayerParameters& aParameters,
     bool aIsForCaret) const;
+  virtual const mozilla::DisplayItemClip* ComputeScrollClip(bool aIsForCaret) const;
 
   // nsIScrollbarMediator
   void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
@@ -843,6 +844,10 @@ public:
   {
     return mHelper.ComputeFrameMetrics(aLayer, aContainerReferenceFrame, aParameters, aIsForCaret);
   }
+  virtual const mozilla::DisplayItemClip* ComputeScrollClip(bool aIsForCaret) const
+  {
+    return mHelper.ComputeScrollClip(aIsForCaret);
+  }
   virtual bool IsIgnoringViewportClipping() const override {
     return mHelper.IsIgnoringViewportClipping();
   }
@@ -1239,6 +1244,10 @@ public:
   {
     return mHelper.ComputeFrameMetrics(aLayer, aContainerReferenceFrame, aParameters, aIsForCaret);
   }
+  virtual const mozilla::DisplayItemClip* ComputeScrollClip(bool aIsForCaret) const
+  {
+    return mHelper.ComputeScrollClip(aIsForCaret);
+  }
   virtual bool IsIgnoringViewportClipping() const override {
     return mHelper.IsIgnoringViewportClipping();
   }

layout/generic/nsIScrollableFrame.h

@@ -446,6 +446,8 @@ public:
    * Whether or not this frame uses containerful scrolling.
    */
   virtual bool UsesContainerScrolling() const = 0;
+
+  virtual const mozilla::DisplayItemClip* ComputeScrollClip(bool aIsForCaret) const = 0;
 };
 
 #endif