Defer CGLFlushDrawable until OSX-requested drawRect to avoid spinning when window is obscured.

content/port/browser/render_widget_host_view_port.h

Index: content/port/browser/render_widget_host_view_port.h
diff --git a/content/port/browser/render_widget_host_view_port.h b/content/port/browser/render_widget_host_view_port.h
index 8ff0c5d5908a00d196041de8d46d1e8452aefdee..2589af73752c8722694c89bd546add87b1901014 100644
--- a/content/port/browser/render_widget_host_view_port.h
+++ b/content/port/browser/render_widget_host_view_port.h
@@ -177,6 +177,9 @@ class CONTENT_EXPORT RenderWidgetHostViewPort : public RenderWidgetHostView {
   virtual bool HasAcceleratedSurface(const gfx::Size& desired_size) = 0;
 
 #if defined(OS_MACOSX)
+  // Called just before GetBackingStore blocks for an updated frame.
+  virtual void AboutToWaitForBackingStoreMsg() = 0;
+
   // Retrieve the bounds of the view, in cocoa view coordinates.
   // If the UI scale factor is 2, |GetViewBounds()| will return a size of e.g.
   // (400, 300) in pixels, while this method will return (200, 150).