Bug 1470267 - Store the visual viewport offset in nsIPresShell. r=botond

Added a data member to nsIPresShell to store the visual viewport offset. APZ
will update the visual viewport offset in the presShell for root scroll frames
on every repaint request.

MozReview-Commit-ID: Ksou43hrE6H

--HG--
extra : rebase_source : 812c88efc7556c4bff2a62834cfaaec6e6945093

gfx/layers/apz/util/APZCCallbackHelper.cpp

@@ -74,6 +74,16 @@ RecenterDisplayPort(mozilla::layers::FrameMetrics& aFrameMetrics)
   aFrameMetrics.SetDisplayPortMargins(margins);
 }
 
+static already_AddRefed<nsIPresShell>
+GetPresShell(const nsIContent* aContent)
+{
+  nsCOMPtr<nsIPresShell> result;
+  if (nsIDocument* doc = aContent->GetComposedDoc()) {
+    result = doc->GetShell();
+  }
+  return result.forget();
+}
+
 static CSSPoint
 ScrollFrameTo(nsIScrollableFrame* aFrame, const FrameMetrics& aMetrics, bool& aSuccessOut)
 {
@@ -146,6 +156,11 @@ ScrollFrame(nsIContent* aContent,
   if (sf) {
     sf->ResetScrollInfoIfGeneration(aMetrics.GetScrollGeneration());
     sf->SetScrollableByAPZ(!aMetrics.IsScrollInfoLayer());
+    if (sf->IsRootScrollFrameOfDocument()) {
+      if (nsCOMPtr<nsIPresShell> shell = GetPresShell(aContent)) {
+        shell->SetVisualViewportOffset(CSSPoint::ToAppUnits(aMetrics.GetScrollOffset()));
+      }
+    }
   }
   bool scrollUpdated = false;
   CSSPoint apzScrollOffset = aMetrics.GetScrollOffset();
@@ -230,16 +245,6 @@ SetDisplayPortMargins(nsIPresShell* aPresShell,
   nsLayoutUtils::SetDisplayPortBaseIfNotSet(aContent, base);
 }
 
-static already_AddRefed<nsIPresShell>
-GetPresShell(const nsIContent* aContent)
-{
-  nsCOMPtr<nsIPresShell> result;
-  if (nsIDocument* doc = aContent->GetComposedDoc()) {
-    result = doc->GetShell();
-  }
-  return result.forget();
-}
-
 static void
 SetPaintRequestTime(nsIContent* aContent, const TimeStamp& aPaintRequestTime)
 {

layout/base/nsIPresShell.h

@@ -1667,6 +1667,14 @@ public:
     return mScrollPositionClampingScrollPortSize;
   }
 
+  void SetVisualViewportOffset(const nsPoint& aScrollOffset) {
+    mVisualViewportOffset = aScrollOffset;
+  }
+
+  nsPoint GetVisualViewportOffset() const {
+    return mVisualViewportOffset;
+  }
+
   virtual void WindowSizeMoveDone() = 0;
   virtual void SysColorChanged() = 0;
   virtual void ThemeChanged() = 0;
@@ -1745,6 +1753,8 @@ protected:
 
   nsSize                    mScrollPositionClampingScrollPortSize;
 
+  nsPoint                   mVisualViewportOffset;
+
   // A list of stack weak frames. This is a pointer to the last item in the list.
   AutoWeakFrame*            mAutoWeakFrames;