Explicitly specify contents scale for SurfaceLayer.

cc/layers/surface_layer.h

Index: cc/layers/surface_layer.h
diff --git a/cc/layers/surface_layer.h b/cc/layers/surface_layer.h
index 29d821f53d3850326b97cc1bf215ad19108feda9..9b7358965b10e81865bf2de4a40f05773ea27160 100644
--- a/cc/layers/surface_layer.h
+++ b/cc/layers/surface_layer.h
@@ -30,7 +30,7 @@ class CC_EXPORT SurfaceLayer : public Layer {
       const SatisfyCallback& satisfy_callback,
       const RequireCallback& require_callback);
 
-  void SetSurfaceId(SurfaceId surface_id, const gfx::Size& size);
+  void SetSurfaceId(SurfaceId surface_id, float scale, const gfx::Size& size);
 
   // Layer overrides.
   scoped_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl) override;
@@ -53,6 +53,7 @@ class CC_EXPORT SurfaceLayer : public Layer {
 
   SurfaceId surface_id_;
   gfx::Size surface_size_;
+  float surface_scale_;
   SurfaceSequence destroy_sequence_;
   SatisfyCallback satisfy_callback_;
   RequireCallback require_callback_;