Make GL calls go through subclassable class.

ui/gl/gl_implementation.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_implementation.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/logging.h"
+#include "ui/gl/gl_bindings.h"
 
 namespace gfx {
 
 namespace {
 
 const struct {
   const char* name;
   GLImplementation implementation;
 } kGLImplementationNamePairs[] = {
   { kGLImplementationDesktopName, kGLImplementationDesktopGL },
@@ skipping 32 matching lines @@
     case kGLImplementationEGLGLES2:
       return false;
     default:
       NOTREACHED();
       return true;
   }
 }
 
 }
 
+GLApi* g_current_gl_context;
+OSMESAApi* g_current_osmesa_context;
+
+#if defined(OS_WIN)
+
+EGLApi* g_current_egl_context;
+WGLApi* g_current_wgl_context;
+
+#elif defined(USE_X11)
+
+EGLApi* g_current_egl_context;
+GLXApi* g_current_glx_context;
+
+#elif defined(OS_ANDROID)
+
+EGLApi* g_current_egl_context;
+
+#endif
+
 GLImplementation GetNamedGLImplementation(const std::string& name) {
   for (size_t i = 0; i < ARRAYSIZE_UNSAFE(kGLImplementationNamePairs); ++i) {
     if (name == kGLImplementationNamePairs[i].name)
       return kGLImplementationNamePairs[i].implementation;
   }
 
   return kGLImplementationNone;
 }
 
 const char* GetGLImplementationName(GLImplementation implementation) {
@@ skipping 67 matching lines @@
   if (!proc && g_get_proc_address) {
     proc = g_get_proc_address(name);
     if (proc)
       return proc;
   }
 
   return proc;
 }
 
 }  // namespace gfx