Enable browser plugin compositing by default, but add a flag to disable it.

content/browser/renderer_host/render_widget_host_view_guest.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_GUEST_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_GUEST_H_
 
 #include <vector>
 
 #include "base/memory/scoped_ptr.h"
@@ skipping 160 matching lines @@
   friend class RenderWidgetHostView;
 
  private:
   // Destroys this view without calling |Destroy| on |platform_view_|.
   void DestroyGuestView();
 
   // The model object.
   RenderWidgetHostImpl* host_;
 
   BrowserPluginGuest *guest_;
-  bool enable_compositing_;
   bool is_hidden_;
   // The platform view for this RenderWidgetHostView.
   // RenderWidgetHostViewGuest mostly only cares about stuff related to
   // compositing, the rest are directly forwared to this |platform_view_|.
   RenderWidgetHostViewPort* platform_view_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostViewGuest);
 };
 
 }  // namespace content
 
 #endif  // CHROME_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_GUEST_H_