We have a problem in the process on destroying WebContentsImpl because

chrome/browser/extensions/api/web_navigation/web_navigation_api.cc

 // 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.
 
 // Implements the Chrome Extensions WebNavigation API.
 
 #include "chrome/browser/extensions/api/web_navigation/web_navigation_api.h"
 
 #include "base/lazy_instance.h"
 #include "chrome/browser/chrome_notification_types.h"
@@ skipping 628 matching lines @@
         web_contents(),
         render_view_host->GetProcess()->GetID(),
         navigation_state_.GetUrl(frame_id),
         frame_num,
         navigation_state_.IsMainFrame(frame_id),
         net::ERR_ABORTED);
   }
   navigation_state_.FrameDetached(frame_id);
 }
 
-void WebNavigationTabObserver::WebContentsDestroyed(content::WebContents* tab) {
-  g_tab_observer.Get().erase(tab);
+void WebNavigationTabObserver::WebContentsDestroyed() {
+  g_tab_observer.Get().erase(web_contents());
   registrar_.RemoveAll();
-  SendErrorEvents(tab, NULL, FrameNavigationState::FrameID());
+  SendErrorEvents(web_contents(), NULL, FrameNavigationState::FrameID());
 }
 
 void WebNavigationTabObserver::SendErrorEvents(
     content::WebContents* web_contents,
     content::RenderViewHost* render_view_host,
     FrameNavigationState::FrameID id_to_skip) {
   for (FrameNavigationState::const_iterator frame = navigation_state_.begin();
        frame != navigation_state_.end(); ++frame) {
     if (!navigation_state_.GetNavigationCompleted(*frame) &&
         navigation_state_.CanSendEvents(*frame) &&
@@ skipping 174 matching lines @@
 
 void WebNavigationAPI::OnListenerAdded(const EventListenerInfo& details) {
   web_navigation_event_router_.reset(new WebNavigationEventRouter(
       Profile::FromBrowserContext(browser_context_)));
   EventRouter::Get(browser_context_)->UnregisterObserver(this);
 }
 
 #endif  // OS_ANDROID
 
 }  // namespace extensions