Make GL calls go through subclassable class.

ui/gl/gl_context_wgl.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.
 
 // This file implements the GLContextWGL and PbufferGLContext classes.
 
 #include "ui/gl/gl_context_wgl.h"
 
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_surface_wgl.h"
 
 namespace gfx {
 
 GLContextWGL::GLContextWGL(GLShareGroup* share_group)
     : GLContext(share_group),
       context_(NULL) {
 }
 
 GLContextWGL::~GLContextWGL() {
   Destroy();
 }
 
 std::string GLContextWGL::GetExtensions() {
   const char* extensions = NULL;
-  if (wglGetExtensionsStringARB)
+  if (g_driver_wgl.fn.wglGetExtensionsStringARBFn)
     extensions = wglGetExtensionsStringARB(GLSurfaceWGL::GetDisplayDC());
-  else if (wglGetExtensionsStringEXT)
+  else if (g_driver_wgl.fn.wglGetExtensionsStringEXTFn)
     extensions = wglGetExtensionsStringEXT();
 
   if (extensions)
     return GLContext::GetExtensions() + " " + extensions;
 
   return GLContext::GetExtensions();
 }
 
 bool GLContextWGL::Initialize(
     GLSurface* compatible_surface, GpuPreference gpu_preference) {
@@ skipping 81 matching lines @@
 
   return true;
 }
 
 void* GLContextWGL::GetHandle() {
   return context_;
 }
 
 void GLContextWGL::SetSwapInterval(int interval) {
   DCHECK(IsCurrent(NULL));
-  if (gfx::g_WGL_EXT_swap_control) {
+  if (gfx::g_driver_wgl.ext.b_WGL_EXT_swap_control) {
     wglSwapIntervalEXT(interval);
   } else {
       LOG(WARNING) <<
           "Could not disable vsync: driver does not "
           "support WGL_EXT_swap_control";
   }
 }
 
 }  // namespace gfx