Add support for accelerated fixed root background

Source/WebCore/page/FrameView.h

Index: Source/WebCore/page/FrameView.h
diff --git a/Source/WebCore/page/FrameView.h b/Source/WebCore/page/FrameView.h
index 07bbb828abc142c99aff204e17b91d4dca01235e..7f1e43c2badf1aba275b3d5fc540d4e992e3e78a 100644
--- a/Source/WebCore/page/FrameView.h
+++ b/Source/WebCore/page/FrameView.h
@@ -217,6 +217,9 @@ public:
     const ViewportConstrainedObjectSet* viewportConstrainedObjects() const { return m_viewportConstrainedObjects.get(); }
     bool hasViewportConstrainedObjects() const { return m_viewportConstrainedObjects && m_viewportConstrainedObjects->size() > 0; }
 
+    void setHasFixedRootBackgroundLayer(bool hasLayer) { m_hasFixedRootBackgroundLayer = hasLayer; }
+    bool hasFixedRootBackgroundLayer() const { return m_hasFixedRootBackgroundLayer; }
+
     // Functions for querying the current scrolled position, negating the effects of overhang
     // and adjusting for page scale.
     IntSize scrollOffsetForFixedPosition() const;
@@ -597,6 +600,7 @@ private:
 
     OwnPtr<ScrollableAreaSet> m_scrollableAreas;
     OwnPtr<ViewportConstrainedObjectSet> m_viewportConstrainedObjects;
+    bool m_hasFixedRootBackgroundLayer;
 
     int m_headerHeight;
     int m_footerHeight;