Plumb ViewportMetrics change notifications around the world and back.

mojo/services/view_manager/public/cpp/lib/view_private.cc

 // 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 "view_manager/public/cpp/lib/view_private.h"
 
 namespace mojo {
 
 ViewPrivate::ViewPrivate(View* view)
     : view_(view) {
+  CHECK(view);
 }
 
 ViewPrivate::~ViewPrivate() {
 }
 
 // static
 View* ViewPrivate::LocalCreate() {
   return new View;
 }
 
 }  // namespace mojo