Add a temporary check to investigate NavigationThrottle crash

content/browser/frame_host/navigation_handle_impl.cc

 // 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.
 
 #include "content/browser/frame_host/navigation_handle_impl.h"
 
 #include <iterator>
 
 #include "base/debug/dump_without_crashing.h"
 #include "base/logging.h"
@@ skipping 1073 matching lines @@
   }
 
   if (!callback.is_null())
     callback.Run(result);
 
   // No code after running the callback, as it might have resulted in our
   // destruction.
 }
 
 void NavigationHandleImpl::RegisterNavigationThrottles() {
+  // TODO(clamy): Remove this when we understand the root cause behind
+  // crbug.com/736658.
+  CHECK(!throttles_have_been_added_);
+  throttles_have_been_added_ = true;
+
   // Register the navigation throttles. The vector returned by
   // CreateThrottlesForNavigation is not assigned to throttles_ directly because
   // it would overwrite any throttles previously added with
   // RegisterThrottleForTesting.
   // TODO(carlosk, arthursonzogni): should simplify this to either use
   // |throttles_| directly (except for the case described above) or
   // |throttles_to_register| for registering all throttles.
   std::vector<std::unique_ptr<NavigationThrottle>> throttles_to_register =
       GetDelegate()->CreateThrottlesForNavigation(this);
 
@@ skipping 80 matching lines @@
   // Stop expecting a navigation to the current site URL in the current expected
   // process.
   SetExpectedProcess(nullptr);
 
   // Update the site URL and the expected process.
   site_url_ = new_site_url;
   SetExpectedProcess(post_redirect_process);
 }
 
 }  // namespace content