Mac Overlays: Allow the primary plane to be optionally scheduled.

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 0bcff6913cfd3d4d6cf875e60d395ea72475e606..e50c9d058a82d08d98d133f38ebd54dda38f8687 100644
--- a/content/common/gpu/image_transport_surface_overlay_mac.h
+++ b/content/common/gpu/image_transport_surface_overlay_mac.h
@@ -65,7 +65,7 @@ class ImageTransportSurfaceOverlayMac : public gfx::GLSurface,
   gfx::SwapResult SwapBuffersInternal(const gfx::Rect& pixel_damage_rect);
 
   void UpdateRootAndPartialDamagePlanes(
-      const std::vector<linked_ptr<OverlayPlane>>& new_overlay_planes,
+      const linked_ptr<OverlayPlane>& new_root_plane,
       const gfx::RectF& dip_damage_rect);
   void UpdateOverlayPlanes(
       const std::vector<linked_ptr<OverlayPlane>>& new_overlay_planes);
@@ -108,8 +108,9 @@ class ImageTransportSurfaceOverlayMac : public gfx::GLSurface,
   // targeting.
   GLint gl_renderer_id_;
 
-  // Overlay planes that have been scheduled, but have not had a subsequent
-  // SwapBuffers call made yet.
+  // Planes that have been scheduled, but have not had a subsequent SwapBuffers
+  // call made yet.
+  linked_ptr<OverlayPlane> pending_root_plane_;
   std::vector<linked_ptr<OverlayPlane>> pending_overlay_planes_;
 
   // A queue of all frames that have been created by SwapBuffersInternal but