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

chrome/browser/ui/views/accelerator_utils_aura.cc

+// 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.
+
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/ui/views/accelerator_table.h"
+#include "ui/base/accelerators/accelerator.h"
+
+#if defined(USE_ASH)
+#include "ash/accelerators/accelerator_table.h"
+#endif  // USE_ASH
+
+namespace chrome {
+
+bool IsChromeAccelerator(const ui::Accelerator& accelerator, Profile* profile) {
+#if defined(USE_ASH)
+  for (size_t i = 0; i < ash::kAcceleratorDataLength; ++i) {
+    const ash::AcceleratorData& accel_data = ash::kAcceleratorData[i];
+    if (accel_data.keycode == accelerator.key_code() &&
+        accel_data.modifiers == accelerator.modifiers()) {
+      return true;
+    }
+  }
+#endif
+
+  std::vector<chrome::AcceleratorMapping> accelerators =
+      chrome::GetAcceleratorList();
+  for (std::vector<chrome::AcceleratorMapping>::const_iterator it =
+       accelerators.begin(); it != accelerators.end(); ++it) {
+    if (it->keycode == accelerator.key_code() &&
+        it->modifiers == accelerator.modifiers())
+      return true;
+  }
+
+  return false;
+}
+
+}  // namespace chrome