Map the render process's glBindFramebuffer(0) to the context's backing FBO....

app/gfx/gl/gl_context.h

 // Copyright (c) 2010 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 APP_GFX_GL_GL_CONTEXT_H_
 #define APP_GFX_GL_GL_CONTEXT_H_
 #pragma once
 
 #include <string>
 
@@ skipping 27 matching lines @@
 
   // Get the size of the back buffer.
   virtual gfx::Size GetSize() = 0;
 
   // Get the underlying platform specific GL context "handle".
   virtual void* GetHandle() = 0;
 
   // Set swap interval. This context must be current.
   virtual void SetSwapInterval(int interval) = 0;
 
+  // Returns the internal frame buffer object name if the context is backed by
+  // FBO. Otherwise returns 0.
+  virtual unsigned int GetBackingFrameBufferObject();
+
   // Returns space separated list of extensions. The context must be current.
   virtual std::string GetExtensions();
 
   // Returns whether the current context supports the named extension. The
   // context must be current.
   bool HasExtension(const char* name);
 
   static bool InitializeOneOff();
 
 #if !defined(OS_MACOSX)
@@ skipping 11 matching lines @@
  protected:
   bool InitializeCommon();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(GLContext);
 };
 
 }  // namespace gfx
 
 #endif  // APP_GFX_GL_GL_CONTEXT_H_