Add "sidebar" section to extension manifest:...

chrome/browser/sidebar/sidebar_manager.cc

 // Copyright (c) 2010 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/sidebar/sidebar_manager.h"
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "chrome/browser/browser_process.h"
@@ skipping 89 matching lines @@
   }
 }
 
 void SidebarManager::ShowSidebar(TabContents* tab,
                                  const std::string& content_id) {
   DCHECK(!content_id.empty());
   SidebarContainer* host = GetSidebarContainerFor(tab, content_id);
   if (!host) {
     host = new SidebarContainer(tab, content_id, this);
     RegisterSidebarContainerFor(tab, host);
+    // It might trigger UpdateSidebar notification, so load them after
+    // the registration.
+    host->LoadDefaults();
   }
 
   host->Show();
 
   ExtensionSidebarEventRouter::OnStateChanged(
       tab->profile(), tab, content_id,
       extension_sidebar_constants::kShownState);
 }
 
 void SidebarManager::ExpandSidebar(TabContents* tab,
@@ skipping 198 matching lines @@
 
   DCHECK(GetSidebarContainerFor(tab, content_id) == sidebar_host);
   DCHECK(sidebar_host_to_tab_.find(sidebar_host)->second == tab);
   DCHECK(tab_to_sidebar_host_[tab].active_content_id != content_id);
 
   tab_to_sidebar_host_[tab].content_id_to_sidebar_host.erase(content_id);
   if (tab_to_sidebar_host_[tab].content_id_to_sidebar_host.empty())
     tab_to_sidebar_host_.erase(tab);
   sidebar_host_to_tab_.erase(sidebar_host);
 }