Add a temporary check to investigate NavigationThrottle crash

content/browser/frame_host/navigation_handle_impl.h

 // Copyright 2015 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.
 
 #ifndef CONTENT_BROWSER_FRAME_HOST_NAVIGATION_HANDLE_IMPL_H_
 #define CONTENT_BROWSER_FRAME_HOST_NAVIGATION_HANDLE_IMPL_H_
 
 #include "content/public/browser/navigation_handle.h"
 
 #include <stddef.h>
@@ skipping 573 matching lines @@
 
   // PlzNavigate
   // Used to inform a RenderProcessHost that we expect this navigation to commit
   // in it.
   int expected_render_process_host_id_;
 
   // TODO(arthursonzogni): Remove this when we understand the root cause behind
   // crbug.com/704892.
   bool is_in_constructor;
 
+  // TODO(clamy): Remove this when we understand the root cause behind
+  // crbug.com/736658.
+  bool throttles_have_been_added_ = false;
+
   base::WeakPtrFactory<NavigationHandleImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(NavigationHandleImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_FRAME_HOST_NAVIGATION_HANDLE_IMPL_H_