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

chrome/browser/ui/accelerator_utils.h

Index: chrome/browser/ui/accelerator_utils.h
diff --git a/chrome/browser/ui/accelerator_utils.h b/chrome/browser/ui/accelerator_utils.h
new file mode 100644
index 0000000000000000000000000000000000000000..8d29e754731057d1b3ed004bc7be8a2de3908c21
--- /dev/null
+++ b/chrome/browser/ui/accelerator_utils.h
@@ -0,0 +1,23 @@
+// Copyright (c) 2013 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.
+
+#ifndef CHROME_BROWSER_UI_ACCELERATOR_UTILS_H_
+#define CHROME_BROWSER_UI_ACCELERATOR_UTILS_H_
+
+class Profile;
+
+namespace ui {
+class Accelerator;
+}
+
+namespace chrome {
+
+// Returns true if the given |accelerator| is currently registered by
+// Chrome.
+bool IsChromeAccelerator(const ui::Accelerator& accelerator,
+                         Profile* profile);
+
+}  // namespace chrome
+
+#endif  // CHROME_BROWSER_UI_ACCELERATOR_UTILS_H_