Implement EXT_draw_buffers WebGL extention support in command buffer.

cc/fake_web_graphics_context_3d.h

 // Copyright 2013 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 CC_FAKE_WEB_GRAPHICS_CONTEXT_3D_H_
 #define CC_FAKE_WEB_GRAPHICS_CONTEXT_3D_H_
 
 #include "base/compiler_specific.h"
 #include "cc/cc_export.h"
 #include "third_party/WebKit/Source/Platform/chromium/public/WebGraphicsContext3D.h"
@@ skipping 564 matching lines @@
   virtual void getQueryObjectuivEXT(
       WebKit::WebGLId query,
       WebKit::WGC3Denum pname,
       WebKit::WGC3Duint* params);
 
   virtual void setContextLostCallback(
       WebGraphicsContextLostCallback* callback);
 
   virtual void loseContextCHROMIUM(WebKit::WGC3Denum current,
                                    WebKit::WGC3Denum other);
+
+  virtual void drawBuffersEXT(WebKit::WGC3Dsizei m,
+                              const WebKit::WGC3Denum* bufs) {}
 };
 
 }  // namespace cc
 
 #endif  // CC_FAKE_WEB_GRAPHICS_CONTEXT_3D_H_