Begin whitelisting specific extensions for global key registration.

chrome/common/extensions/docs/templates/intros/commands.html

 <h2 id="manifest">Manifest</h2>
 <p>
 You must have a <code>"manifest_version"</code> of at least <code>2</code> to use this API.
 </p>
 
 {{?is_apps +partials.warning_dev /}}
 
 <h2 id="usage">Usage</h2>
 <p>The commands API allows you to define specific commands, and bind them to a
 default key combination. Each command your extension accepts must be listed in
 the manifest as an attribute of the 'commands' manifest key. An extension can
 have many commands but only 4 suggested keys can be specified. The user can
 manually add more shortcuts from the chrome://extensions/configureCommands
 dialog.</p>
 
 <p>Supported keys: A-Z, 0-9, Comma, Period, Home, End, PageUp, PageDown, Insert,
 Delete, Arrow keys (Up, Down, Left, Right) and the Media Keys
 (MediaNextTrack, MediaPlayPause, MediaPrevTrack, MediaStop).</p>
 
 <p>Note: All key combinations must include either Ctrl* or Alt. Combinations
 that involve Ctrl+Alt are not permitted in order to avoid conflicts with the
 AltGr key. Shift can be used in addition to Alt or Ctrl, but is not required.
 Modifiers (such as Ctrl) can not be used in combination with the Media Keys.
 Tab key was removed from list of supported keys in Chrome version 33 and above
 for accessibility reasons.<p>
 
 <p>* Also note that on Mac 'Ctrl' is automatically converted to 'Command'. If
 you want 'Ctrl' instead, please specify 'MacCtrl'.</p>
 
+<p>* Additionally, on Chrome OS, you can specify Search as a modifier.</p>
+
 <p>Certain Chrome shortcuts (e.g. window management) always take priority over
 Extension Command shortcuts and can not be overwritten.</p>
 
 <pre data-filename="manifest.json">
 {
   "name": "My extension",
   ...
 <b>  "commands": {
     "toggle-feature-foo": {
       "suggested_key": {
@@ skipping 62 matching lines @@
     "toggle-feature-foo": {
       "suggested_key": {
         "default": "Ctrl+Shift+5"
       },
       "description": "Toggle feature foo",
       <b>"global": true</b>
     }
   },
   ...
 }</pre>