Make sure manifest specified shortcut for Extension Command can not override the built-in shortcuts.

chrome/browser/ui/views/frame/browser_view.cc

 // Copyright 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/views/frame/browser_view.h"
 
 #include <algorithm>
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
@@ skipping 620 matching lines @@
     if (it->second == cmd_id) {
       *accelerator = it->first;
       return true;
     }
   }
   // Else, we retrieve the accelerator information from Ash (if applicable).
   return chrome::GetAshAcceleratorForCommandId(
       cmd_id, browser_->host_desktop_type(), accelerator);
 }
 
+bool BrowserView::IsAcceleratorRegistered(const ui::Accelerator& accelerator) {
+  return accelerator_table_.find(accelerator) != accelerator_table_.end();
+}
+
 WebContents* BrowserView::GetActiveWebContents() const {
   return browser_->tab_strip_model()->GetActiveWebContents();
 }
 
 gfx::ImageSkia BrowserView::GetOTRAvatarIcon() const {
   return *GetThemeProvider()->GetImageSkiaNamed(GetOTRIconResourceID());
 }
 
 bool BrowserView::IsPositionInWindowCaption(const gfx::Point& point) {
   if (window_switcher_button_) {
@@ skipping 2074 matching lines @@
 
   Browser* modal_browser =
       chrome::FindBrowserWithWebContents(active_dialog->web_contents());
   if (modal_browser && (browser_ != modal_browser)) {
     modal_browser->window()->FlashFrame(true);
     modal_browser->window()->Activate();
   }
 
   AppModalDialogQueue::GetInstance()->ActivateModalDialog();
 }