Switch WebNavigationTabObserver to use WebContentsUserData.

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/extensions/api/web_navigation/web_navigation_api_constants.h"
@@ skipping 235 matching lines @@
            pending_web_contents_.begin(); i != pending_web_contents_.end(); ) {
     if (i->second.source_web_contents == tab)
       pending_web_contents_.erase(i++);
     else
       ++i;
   }
 }
 
 // WebNavigationTabObserver ------------------------------------------
 
+int WebNavigationTabObserver::kUserDataKey;
+
 WebNavigationTabObserver::WebNavigationTabObserver(
     content::WebContents* web_contents)
     : WebContentsObserver(web_contents),
       render_view_host_(NULL),
       pending_render_view_host_(NULL) {
   g_tab_observer.Get().insert(TabObserverMap::value_type(web_contents, this));
   registrar_.Add(this,
                  content::NOTIFICATION_RESOURCE_RECEIVED_REDIRECT,
                  content::Source<content::WebContents>(web_contents));
   registrar_.Add(this,
@@ skipping 454 matching lines @@
         navigation_state.IsMainFrame(frame_id), frame_id.frame_num);
     frame->process_id = frame_id.render_view_host->GetProcess()->GetID();
     frame->error_occurred = navigation_state.GetErrorOccurredInFrame(frame_id);
     result_list.push_back(frame);
   }
   results_ = GetAllFrames::Results::Create(result_list);
   return true;
 }
 
 }  // namespace extensions