Paint solid color background into both scrolling contents layer and graphics layer.

third_party/WebKit/Source/core/paint/PaintLayer.h

Index: third_party/WebKit/Source/core/paint/PaintLayer.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.h b/third_party/WebKit/Source/core/paint/PaintLayer.h
index 1789db0506d17d184607e56ad157c3123ec4c4cc..e4606800f39731e5c0e47e0ff0838426d8f76545 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -503,12 +503,11 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
   CompositedLayerMapping* compositedLayerMapping() const;
   GraphicsLayer* graphicsLayerBacking() const;
   GraphicsLayer* graphicsLayerBackingForScrolling() const;
-  // Returns true for layers with scrollable overflow which have a background
-  // that can be painted into the composited scrolling contents layer when it
-  // exist (i.e. the background can scroll with the content). When the
-  // background is also opaque this allows us to composite the scroller even on
+  // Returns which layers backgrounds should be painted into for overflow

[chrishtr, 2016/11/17 20:55:39]

s/layers/GraphicsLayers

[flackr, 2016/11/17 23:38:00]

Done.

+  // scrolling boxes. When the background can paint into the scrolling contents
+  // and is also opaque this allows us to composite the scroller even on
   // low DPI as we can draw with subpixel anti-aliasing.
-  bool canPaintBackgroundOntoScrollingContentsLayer() const;
+  BackgroundPaintLocation backgroundPaintLocation() const;
   // NOTE: If you are using hasCompositedLayerMapping to determine the state of
   // compositing for this layer, (and not just to do bookkeeping related to the
   // mapping like, say, allocating or deallocating a mapping), then you may have