Make GL calls go through subclassable class.

ui/gl/gl_surface_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.
 
 #include "ui/gl/gl_surface_wgl.h"
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/gl/gl_bindings.h"
+#include "ui/gl/gl_gl_api_implementation.h"
+#include "ui/gl/gl_wgl_api_implementation.h"
 
 namespace gfx {
 
 namespace {
 const PIXELFORMATDESCRIPTOR kPixelFormatDescriptor = {
   sizeof(kPixelFormatDescriptor),    // Size of structure.
   1,                       // Default version.
   PFD_DRAW_TO_WINDOW |     // Window drawing support.
   PFD_SUPPORT_OPENGL |     // OpenGL support.
   PFD_DOUBLEBUFFER,        // Double buffering support (not stereo).
@@ skipping 279 matching lines @@
       pbuffer_(NULL) {
 }
 
 PbufferGLSurfaceWGL::~PbufferGLSurfaceWGL() {
   Destroy();
 }
 
 bool PbufferGLSurfaceWGL::Initialize() {
   DCHECK(!device_context_);
 
-  if (!wglCreatePbufferARB) {
+  if (!gfx::g_driver_wgl.fn.wglCreatePbufferARBFn) {
     LOG(ERROR) << "wglCreatePbufferARB not available.";
     Destroy();
     return false;
   }
 
   const int kNoAttributes[] = { 0 };
   pbuffer_ = wglCreatePbufferARB(g_display->device_context(),
                                  g_display->pixel_format(),
                                  size_.width(), size_.height(),
                                  kNoAttributes);
@@ skipping 37 matching lines @@
 
 gfx::Size PbufferGLSurfaceWGL::GetSize() {
   return size_;
 }
 
 void* PbufferGLSurfaceWGL::GetHandle() {
   return device_context_;
 }
 
 }  // namespace gfx