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

ui/gl/gl_implementation_mac.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 "base/base_paths.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/mac/foundation_util.h"
 #include "base/native_library.h"
 #include "base/path_service.h"
@@ skipping 13 matching lines @@
 void GetAllowedGLImplementations(std::vector<GLImplementation>* impls) {
   impls->push_back(kGLImplementationDesktopGL);
   impls->push_back(kGLImplementationAppleGL);
   impls->push_back(kGLImplementationOSMesaGL);
 }
 
 bool InitializeStaticGLBindings(GLImplementation implementation) {
   // Prevent reinitialization with a different implementation. Once the gpu
   // unit tests have initialized with kGLImplementationMock, we don't want to
   // later switch to another GL implementation.
-  if (GetGLImplementation() != kGLImplementationNone)
-    return true;
+  DCHECK_EQ(kGLImplementationNone, GetGLImplementation());
 
   // Allow the main thread or another to initialize these bindings
   // after instituting restrictions on I/O. Going forward they will
   // likely be used in the browser process on most platforms. The
   // one-time initialization cost is small, between 2 and 5 ms.
   base::ThreadRestrictions::ScopedAllowIO allow_io;
 
   switch (implementation) {
     case kGLImplementationOSMesaGL: {
       // osmesa.so is located in the build directory. This code path is only
@@ skipping 101 matching lines @@
   SetGLImplementation(kGLImplementationNone);
 
   UnloadGLNativeLibraries();
 }
 
 bool GetGLWindowSystemBindingInfo(GLWindowSystemBindingInfo* info) {
   return false;
 }
 
 }  // namespace gfx