Ensure GL initialization only happens once, and provide common init path

ui/gl/gl_gl_api_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_gl_api_implementation.h"
 
 #include <algorithm>
 #include <vector>
 
 #include "base/command_line.h"
@@ skipping 128 matching lines @@
 static void GL_BINDING_CALL CustomRenderbufferStorageMultisampleEXT(
     GLenum target, GLsizei samples, GLenum internalformat, GLsizei width,
     GLsizei height) {
   GLenum gl_internal_format = GetInternalFormat(internalformat);
   return g_driver_gl.orig_fn.glRenderbufferStorageMultisampleEXTFn(
       target, samples, gl_internal_format, width, height);
 }
 
 }  // anonymous namespace
 
+DriverGL::DriverGL() { ClearBindings(); }
+
 void DriverGL::InitializeCustomDynamicBindings(GLContext* context) {
   InitializeDynamicBindings(context);
-  orig_fn = fn;
+
+  DCHECK(orig_fn.glTexImage2DFn == NULL);
+  orig_fn.glTexImage2DFn = fn.glTexImage2DFn;
   fn.glTexImage2DFn =
       reinterpret_cast<glTexImage2DProc>(CustomTexImage2D);
+
+  DCHECK(orig_fn.glTexSubImage2DFn == NULL);
+  orig_fn.glTexSubImage2DFn = fn.glTexSubImage2DFn;
   fn.glTexSubImage2DFn =
       reinterpret_cast<glTexSubImage2DProc>(CustomTexSubImage2D);
+
+  DCHECK(orig_fn.glTexStorage2DEXTFn == NULL);
+  orig_fn.glTexStorage2DEXTFn = fn.glTexStorage2DEXTFn;
   fn.glTexStorage2DEXTFn =
       reinterpret_cast<glTexStorage2DEXTProc>(CustomTexStorage2DEXT);
+
+  DCHECK(orig_fn.glRenderbufferStorageEXTFn == NULL);
+  orig_fn.glRenderbufferStorageEXTFn = fn.glRenderbufferStorageEXTFn;
   fn.glRenderbufferStorageEXTFn =
       reinterpret_cast<glRenderbufferStorageEXTProc>(
       CustomRenderbufferStorageEXT);
+
+  DCHECK(orig_fn.glRenderbufferStorageMultisampleEXTFn == NULL);
+  orig_fn.glRenderbufferStorageMultisampleEXTFn =
+      fn.glRenderbufferStorageMultisampleEXTFn;
   fn.glRenderbufferStorageMultisampleEXTFn =
       reinterpret_cast<glRenderbufferStorageMultisampleEXTProc>(
       CustomRenderbufferStorageMultisampleEXT);
 }
 
 void InitializeStaticGLBindingsGL() {
   g_current_gl_context_tls = new base::ThreadLocalPointer<GLApi>;
   g_driver_gl.InitializeStaticBindings();
   if (!g_real_gl) {
     g_real_gl = new RealGLApi();
@@ skipping 164 matching lines @@
 const GLubyte* VirtualGLApi::glGetStringFn(GLenum name) {
   switch (name) {
     case GL_EXTENSIONS:
       return reinterpret_cast<const GLubyte*>(extensions_.c_str());
     default:
       return driver_->fn.glGetStringFn(name);
   }
 }
 
 }  // namespace gfx