Delete background tab IOSurfaces on Mac.

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 cf0d4594de564ee96dec1b27174fb42e12a5c5e9..082c70f3ecd602ac2a39c6f404e9743e2b7bf143 100644
--- a/content/port/browser/render_widget_host_view_port.h
+++ b/content/port/browser/render_widget_host_view_port.h
@@ -175,6 +175,14 @@ class CONTENT_EXPORT RenderWidgetHostViewPort : public RenderWidgetHostView {
   // next swap buffers or post sub buffer.
   virtual void AcceleratedSurfaceSuspend() = 0;
 
+  // Return true if the view has an accelerated surface that contains the last
+  // presented frame for the view. If |desired_size| is non-empty, true is
+  // returned only if the accelerated surface size matches.
+  virtual bool HasAcceleratedSurface(const gfx::Size& desired_size) = 0;
+
+  // Called just before GetBackingStore blocks for an UpdateRect message.
+  virtual void AboutToWaitForUpdateMsg() {}
+
 #if defined(OS_MACOSX)
   // 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.