Mac: Enable partial swap

content/common/gpu/image_transport_surface_overlay_mac.h

Index: content/common/gpu/image_transport_surface_overlay_mac.h
diff --git a/content/common/gpu/image_transport_surface_overlay_mac.h b/content/common/gpu/image_transport_surface_overlay_mac.h
index 022fbb41e7922a9c8e607529348033b12842f3c0..1265cc408baf80bede020766afe1ea655025800c 100644
--- a/content/common/gpu/image_transport_surface_overlay_mac.h
+++ b/content/common/gpu/image_transport_surface_overlay_mac.h
@@ -79,6 +79,7 @@ class ImageTransportSurfaceOverlayMac : public gfx::GLSurface,
   scoped_ptr<ImageTransportHelper> helper_;
   base::scoped_nsobject<CAContext> ca_context_;
   base::scoped_nsobject<CALayer> layer_;
+  base::scoped_nsobject<CALayer> partial_damage_layer_;
 
   gfx::Size pixel_size_;
   float scale_factor_;
@@ -94,6 +95,10 @@ class ImageTransportSurfaceOverlayMac : public gfx::GLSurface,
   // every swap and also by a callback.
   std::deque<linked_ptr<PendingSwap>> pending_swaps_;
 
+  // The union of the damage rects of SwapBuffersInternal since the last
+  // non-partial swap.
+  gfx::Rect accumulated_partial_damage_pixel_rect_;
+
   // The display link used to compute the time for callbacks.
   scoped_refptr<ui::DisplayLinkMac> display_link_mac_;