Use stub GL draw/clear calls for browser tests that do not need pixels.

ui/gl/gl_gl_api_implementation.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 UI_GL_GL_API_IMPLEMENTATION_H_
 #define UI_GL_GL_API_IMPLEMENTATION_H_
 
 #include "base/compiler_specific.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_export.h"
 
 namespace gpu {
 namespace gles2 {
 class GLES2Decoder;
 }
 }
 namespace gfx {
 
 class GLContext;
 class GLSurface;
 
 void InitializeGLBindingsGL();
 void InitializeGLExtensionBindingsGL(GLContext* context);
 void InitializeDebugGLBindingsGL();
+void InitializeStubGLBindingsGL();
 void ClearGLBindingsGL();
 void SetGLToRealGLApi();
 void SetGLApi(GLApi* api);
 
 class GL_EXPORT GLApiBase : public GLApi {
  public:
   // Include the auto-generated part of this class. We split this because
   // it means we can easily edit the non-auto generated parts right here in
   // this file instead of having to edit some template or the code generator.
   #include "gl_bindings_api_autogen_gl.h"
@@ skipping 53 matching lines @@
   // The current virtual context.
   GLContext* current_context_;
 
   // The supported extensions being advertised for this virtual context.
   std::string extensions_;
 };
 
 }  // namespace gfx
 
 #endif  // UI_GL_GL_API_IMPLEMENTATION_H_