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

chrome/browser/ui/cocoa/accelerator_utils_cocoa.mm

+// 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/cocoa/accelerators_cocoa.h"
+#import "chrome/browser/ui/cocoa/browser_window_utils.h"
+#include "content/public/browser/native_web_keyboard_event.h"
+#include "ui/base/accelerators/accelerator.h"
+#import "ui/base/accelerators/platform_accelerator_cocoa.h"
+#import "ui/base/keycodes/keyboard_code_conversion_mac.h"
+
+namespace chrome {
+
+bool IsChromeAccelerator(const ui::Accelerator& accelerator, Profile* profile) {
+  // The |accelerator| passed in contains a Windows key code but no platform
+  // accelerator info. The Accelerator list is the opposite: It has accelerators
+  // that have key_code() == VKEY_UNKNOWN but they contain a platform
+  // accelerator. We find common ground by converting the passed in Windows key
+  // code to a character and use that when comparing against the Accelerator
+  // list.
+  unichar character;
+  unichar characterIgnoringModifiers;
+  ui::MacKeyCodeForWindowsKeyCode(accelerator.key_code(),
+                                  0,
+                                  &character,
+                                  &characterIgnoringModifiers);
+  NSString* characters =
+      [[[NSString alloc] initWithCharacters:&character length:1] autorelease];
+
+  NSUInteger modifiers =
+      (accelerator.IsCtrlDown() ? NSControlKeyMask : 0) |
+      (accelerator.IsCmdDown() ? NSCommandKeyMask : 0) |
+      (accelerator.IsAltDown() ? NSAlternateKeyMask : 0) |
+      (accelerator.IsShiftDown() ? NSShiftKeyMask : 0);
+
+  NSEvent* event = [NSEvent keyEventWithType:NSKeyDown
+                                    location:NSZeroPoint
+                               modifierFlags:modifiers
+                                   timestamp:0
+                                windowNumber:0
+                                     context:nil
+                                  characters:characters
+                 charactersIgnoringModifiers:characters
+                                   isARepeat:NO
+                                     keyCode:accelerator.key_code()];
+
+  content::NativeWebKeyboardEvent keyboard_event(event);
+  int id = [BrowserWindowUtils getCommandId:keyboard_event];
+  return id != -1;
+}
+
+}  // namespace chrome