Refactor GL bindings so there is no global GLApi or DriverGL.

ui/gl/init/gl_initializer_mac.cc

 // Copyright 2016 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 "ui/gl/init/gl_initializer.h"
 
 #include <OpenGL/CGLRenderers.h>
 
 #include <vector>
 
@@ skipping 145 matching lines @@
   base::ThreadRestrictions::ScopedAllowIO allow_io;
 
   switch (implementation) {
     case kGLImplementationOSMesaGL:
       return InitializeStaticOSMesaInternal();
     case kGLImplementationDesktopGL:
     case kGLImplementationDesktopGLCoreProfile:
     case kGLImplementationAppleGL:
       return InitializeStaticCGLInternal(implementation);
     case kGLImplementationMockGL:
-      SetGLImplementation(kGLImplementationMockGL);
+    case kGLImplementationStubGL:
+      SetGLImplementation(implementation);
       InitializeStaticGLBindingsGL();
       return true;
     default:
       NOTREACHED();
   }
 
   return false;
 }
 
 void InitializeDebugGLBindings() {
   InitializeDebugGLBindingsGL();
   InitializeDebugGLBindingsOSMESA();
 }
 
 void ShutdownGLPlatform() {
   ClearBindingsGL();
   ClearBindingsOSMESA();
 }
 
 }  // namespace init
 }  // namespace gl