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

ui/gl/gl_implementation_ozone.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/bind.h"
 #include "ui/gfx/ozone/surface_factory_ozone.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_context_stub_with_extensions.h"
 #include "ui/gl/gl_egl_api_implementation.h"
 #include "ui/gl/gl_gl_api_implementation.h"
@@ skipping 19 matching lines @@
 
 void GetAllowedGLImplementations(std::vector<GLImplementation>* impls) {
   impls->push_back(kGLImplementationEGLGLES2);
   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());
 
   switch (implementation) {
     case kGLImplementationOSMesaGL:
       return InitializeStaticGLBindingsOSMesaGL();
     case kGLImplementationEGLGLES2:
       ui::OzonePlatform::Initialize();
       if (!gfx::SurfaceFactoryOzone::GetInstance()->LoadEGLGLES2Bindings(
               base::Bind(&AddGLNativeLibrary),
               base::Bind(&SetGLGetProcAddressProc)))
         return false;
@@ skipping 61 matching lines @@
   switch (GetGLImplementation()) {
     case kGLImplementationEGLGLES2:
       return GetGLWindowSystemBindingInfoEGL(info);
     default:
       return false;
   }
   return false;
 }
 
 }  // namespace gfx