Fixes bug where recreating the document element via altering |documentElement...

chrome/browser/extensions/extension_host.cc

 // Copyright (c) 2006-2009 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/extensions/extension_host.h"
 
 #include <list>
 
 #include "app/l10n_util.h"
 #include "app/resource_bundle.h"
@@ skipping 337 matching lines @@
       UMA_HISTOGRAM_TIMES("Extensions.PopupLoadTime",
                           since_created_.Elapsed());
     } else if (extension_host_type_ == ViewType::EXTENSION_TOOLSTRIP) {
       UMA_HISTOGRAM_TIMES("Extensions.ToolstripLoadTime",
                           since_created_.Elapsed());
     }
   }
 }
 
 void ExtensionHost::DocumentAvailableInMainFrame(RenderViewHost* rvh) {
+  // If the document has already been marked as available for this host, then
+  // bail. No need for the redundant setup. http://crbug.com/31170
+  if (document_element_available_)
+    return;
+
   document_element_available_ = true;
   if (is_background_page()) {
     extension_->SetBackgroundPageReady();
   } else {
     InsertThemeCSS();
 
     // Listen for browser changes so we can resend the CSS.
     registrar_.Add(this, NotificationType::BROWSER_THEME_CHANGED,
                    NotificationService::AllSources());
   }
@@ skipping 257 matching lines @@
     // Extensions hosted in ExternalTabContainer objects may not have
     // an associated browser.
     Browser* browser = GetBrowser();
     if (browser)
       window_id = ExtensionTabUtil::GetWindowId(browser);
   } else if (extension_host_type_ != ViewType::EXTENSION_BACKGROUND_PAGE) {
     NOTREACHED();
   }
   return window_id;
 }