Preliminary compositor disabling patch.

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index 1c64453f1be9570e6f4862205da1150d879074e4..14c2299c7b62d30253e76ea1a17cb33d521ba01a 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -504,6 +504,8 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
   // Note this rect is in layer space (not content space).
   void SetUpdateRect(const gfx::Rect& update_rect);
   gfx::Rect update_rect() const { return update_rect_; }
+  void SetOverlayUpdateRect(const gfx::Rect& overlay_update_rect);
+  gfx::Rect overlay_update_rect() const { return overlay_update_rect_; }
 
   void AddDamageRect(const gfx::RectF& damage_rect);
 
@@ -748,6 +750,9 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
   // Uses layer (not content) space.
   gfx::Rect update_rect_;
 
+  // Rect indicating what was updated for an overlayable layer.
+  gfx::Rect overlay_update_rect_;
+
   // This rect is in layer space.
   gfx::RectF damage_rect_;