Invalidate scrolling contents layer on background invalidations painted into it.

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
index d711756d54562d7250b909c4447cd828cbde4716..a46b0590b42b82d7a4ae2f3658078f8b95f14a6c 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
@@ -219,6 +219,13 @@ public:
 
     void adjustForCompositedScrolling(const GraphicsLayer*, IntSize& offset) const;
 
+    // Returns true for layers with scrollable overflow which have a background
+    // that can be painted into the composited scrolling contents layer (i.e.
+    // the background can scroll with the content). When the background is also
+    // opaque this allows us to composite the scroller even on low DPI as we can
+    // draw with subpixel anti-aliasing.
+    bool shouldPaintBackgroundOntoScrollingContentsLayer() const;
+
 private:
     IntRect recomputeInterestRect(const GraphicsLayer*) const;
     static bool interestRectChangedEnoughToRepaint(const IntRect& previousInterestRect, const IntRect& newInterestRect, const IntSize& layerSize);
@@ -329,13 +336,6 @@ private:
     // not appear earlier in the set of layers for this object.
     bool invalidateLayerIfNoPrecedingEntry(size_t);
 
-    // Returns true for layers with scrollable overflow which have a background
-    // that can be painted into the composited scrolling contents layer (i.e.
-    // the background can scroll with the content). When the background is also
-    // opaque this allows us to composite the scroller even on low DPI as we can
-    // draw with subpixel anti-aliasing.
-    bool shouldPaintBackgroundOntoScrollingContentsLayer() const;
-
     PaintLayer& m_owningLayer;
 
     // The hierarchy of layers that is maintained by the CompositedLayerMapping looks like this: