Mac Overlays: Add sandwich strategy

cc/output/output_surface.h

Index: cc/output/output_surface.h
diff --git a/cc/output/output_surface.h b/cc/output/output_surface.h
index 7d0a5d97a15823b91785afbf82bda91b9bae429a..9611ef4406e0fd18514c89a585d40f9f898085f2 100644
--- a/cc/output/output_surface.h
+++ b/cc/output/output_surface.h
@@ -120,7 +120,8 @@ class CC_EXPORT OutputSurface {
   virtual void DiscardBackbuffer();
 
   virtual void Reshape(const gfx::Size& size, float scale_factor);
-  virtual gfx::Size SurfaceSize() const;
+  gfx::Size SurfaceSize() const { return surface_size_; }
+  float device_scale_factor() const { return device_scale_factor_; }
 
   // If supported, this causes a ReclaimResources for all resources that are
   // currently in use.
@@ -145,6 +146,9 @@ class CC_EXPORT OutputSurface {
   // Get the class capable of informing cc of hardware overlay capability.
   virtual OverlayCandidateValidator* GetOverlayCandidateValidator() const;
 
+  // Get the texture for the main image's overlay.
+  virtual unsigned GetOverlayTextureId() const;
+
   void DidLoseOutputSurface();
   void SetMemoryPolicy(const ManagedMemoryPolicy& policy);