[Panels refactor] Track Panels in TaskManager now that they are not under the tab contents umbrella.

chrome/browser/ui/panels/panel_host.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.
 
 #include "chrome/browser/ui/panels/panel_host.h"
 
 #include "base/logging.h"
 #include "base/message_loop.h"
 #include "chrome/browser/chrome_page_zoom.h"
 #include "chrome/browser/favicon/favicon_tab_helper.h"
@@ skipping 40 matching lines @@
   content::WebContentsObserver::Observe(web_contents_.get());
 
   favicon_tab_helper_.reset(new FaviconTabHelper(web_contents_.get()));
 
   web_contents_->GetController().LoadURL(
       url, content::Referrer(), content::PAGE_TRANSITION_LINK, std::string());
 }
 
 void PanelHost::DestroyWebContents() {
   web_contents_.reset();
+  favicon_tab_helper_.reset();
 }
 
 SkBitmap PanelHost::GetPageIcon() const {
   return favicon_tab_helper_.get() ?
       favicon_tab_helper_->GetFavicon() : SkBitmap();
 }
 
 void PanelHost::NavigationStateChanged(const content::WebContents* source,
                                        unsigned changed_flags) {
   // Only need to update the title if the title changed while not loading,
@@ skipping 109 matching lines @@
 }
 
 void PanelHost::StopLoading() {
   content::RecordAction(UserMetricsAction("Stop"));
   web_contents_->Stop();
 }
 
 void PanelHost::Zoom(content::PageZoom zoom) {
   chrome_page_zoom::Zoom(web_contents_.get(), zoom);
 }