Fix flattening for scrollable areas.

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

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index c7c5c88f0d89e53fa86cfda45911f611adf2af21..2f9a9dbc0c1a20f73de8b742c3e6723d7cf3b196 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -1507,12 +1507,13 @@ void CompositedLayerMapping::updateShouldFlattenTransform()
         }, ApplyToChildContainingLayers);
     }
 
-    // Regardless, mark the scrolling contents layer and scrolling block
+    // Regardless, mark the graphics layer, scrolling layer and scrolling block
     // selection layer (if they exist) as not flattening. Having them flatten
     // causes unclipped render surfaces which cause bugs.
     // http://crbug.com/521768
     if (hasScrollingLayer()) {
-        m_scrollingContentsLayer->setShouldFlattenTransform(false);
+        m_graphicsLayer->setShouldFlattenTransform(false);
+        m_scrollingLayer->setShouldFlattenTransform(false);
         if (m_scrollingBlockSelectionLayer)
             m_scrollingBlockSelectionLayer->setShouldFlattenTransform(false);
     }