Make GL calls go through subclassable class.

ui/gl/gl_implementation_mac.cc

 // 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.
 
 #include "base/base_paths.h"
 #include "base/file_path.h"
 #include "base/logging.h"
 #include "base/mac/foundation_util.h"
 #include "base/native_library.h"
 #include "base/path_service.h"
 #include "base/threading/thread_restrictions.h"
 #include "ui/gl/gl_bindings.h"
+#include "ui/gl/gl_gl_api_implementation.h"
 #include "ui/gl/gl_implementation.h"
+#include "ui/gl/gl_osmesa_api_implementation.h"
 
 namespace gfx {
 namespace {
 const char kOpenGLFrameworkPath[] =
     "/System/Library/Frameworks/OpenGL.framework/Versions/Current/OpenGL";
 }  // namespace
 
 void GetAllowedGLImplementations(std::vector<GLImplementation>* impls) {
   impls->push_back(kGLImplementationDesktopGL);
   impls->push_back(kGLImplementationAppleGL);
@@ skipping 107 matching lines @@
 
 void ClearGLBindings() {
   ClearGLBindingsGL();
   ClearGLBindingsOSMESA();
   SetGLImplementation(kGLImplementationNone);
 
   UnloadGLNativeLibraries();
 }
 
 }  // namespace gfx