Perform navigation policy check on UI thread for --site-per-process.

content/browser/frame_host/navigator.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 "content/browser/frame_host/navigator.h"
 
 #include "base/time/time.h"
 
 namespace content {
 
+NavigationController* Navigator::GetController() {
+  return NULL;
+}
+
 bool Navigator::NavigateToPendingEntry(
     RenderFrameHostImpl* render_frame_host,
     NavigationController::ReloadType reload_type) {
   return false;
 }
 
 base::TimeTicks Navigator::GetCurrentLoadStart() {
   return base::TimeTicks::Now();
 }
 
 }  // namespace content