Fix gpu_ipc_service_unittests on mac_chromium_rel_ng by managing GL shared groups the same way in s…

ui/gl/gl_context_mac.mm

 // 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 <memory>
 
 #include "base/logging.h"
 #include "base/trace_event/trace_event.h"
 #include "ui/gl/gl_context_cgl.h"
 #include "ui/gl/gl_context_osmesa.h"
@@ skipping 27 matching lines @@
       return context;
     }
     case kGLImplementationOSMesaGL: {
       scoped_refptr<GLContext> context(new GLContextOSMesa(share_group));
       if (!context->Initialize(compatible_surface, gpu_preference))
         return NULL;
 
       return context;
     }
     case kGLImplementationMockGL:
-      return new GLContextStub;
+      return new GLContextStub(share_group);
     default:
       NOTREACHED();
       return NULL;
   }
 }
 
 }  // namespace gfx