Refactor GL bindings so there is no global GLApi or DriverGL.

gpu/ipc/service/image_transport_surface_mac.mm

 // Copyright 2014 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 "gpu/ipc/service/image_transport_surface.h"
 
 #include "base/macros.h"
 #include "gpu/ipc/service/image_transport_surface_overlay_mac.h"
 #include "gpu/ipc/service/pass_through_image_transport_surface.h"
 #include "ui/gfx/native_widget_types.h"
@@ skipping 37 matching lines @@
     gl::GLSurfaceFormat format) {
   DCHECK_NE(surface_handle, kNullSurfaceHandle);
 
   switch (gl::GetGLImplementation()) {
     case gl::kGLImplementationDesktopGL:
     case gl::kGLImplementationDesktopGLCoreProfile:
     case gl::kGLImplementationAppleGL:
       return make_scoped_refptr<gl::GLSurface>(
           new ImageTransportSurfaceOverlayMac(delegate));
     case gl::kGLImplementationMockGL:
+    case gl::kGLImplementationStubGL:
       return make_scoped_refptr<gl::GLSurface>(new gl::GLSurfaceStub);
     default:
       // Content shell in DRT mode spins up a gpu process which needs an
       // image transport surface, but that surface isn't used to read pixel
       // baselines. So this is mostly a dummy surface.
       if (!g_allow_os_mesa) {
         NOTREACHED();
         return nullptr;
       }
       scoped_refptr<gl::GLSurface> surface(new DRTSurfaceOSMesa());
       if (!surface.get() || !surface->Initialize(format))
         return surface;
       return make_scoped_refptr<gl::GLSurface>(
           new PassThroughImageTransportSurface(delegate, surface.get()));
   }
 }
 
 // static
 void ImageTransportSurface::SetAllowOSMesaForTesting(bool allow) {
   g_allow_os_mesa = allow;
 }
 
 }  // namespace gpu