Play a chime when the hotword is triggered.

chrome/browser/resources/hotword/state_manager.js

 // Copyright (c) 2014 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.
 
 cr.define('hotword', function() {
   'use strict';
 
   /**
    * Class to manage hotwording state. Starts/stops the hotword detector based
    * on user settings, session requests, and any other factors that play into
@@ skipping 25 matching lines @@
      * @private {?hotword.constants.SessionSource}
      */
     this.sessionSource_ = null;
 
     /**
      * Callback to run when the hotword detector has successfully started.
      * @private {!function()}
      */
     this.sessionStartedCb_ = null;
 
+    /**
+     * Hotword trigger audio notification... a.k.a The Chime (tm).
+     * @private {!Audio}
+     */
+    this.chime_ = document.createElement('audio');
+
     // Get the initial status.
     chrome.hotwordPrivate.getStatus(this.handleStatus_.bind(this));
+
+    // Setup the chime and insert into the page.
+    this.chime_.src = chrome.extension.getURL(
+        hotword.constants.SHARED_MODULE_ROOT + '/audio/chime.wav');
+    document.body.appendChild(this.chime_);

[Dan Beam, 2014/09/23 03:43:13]

what happens if this fails to load?

[Anand Mistry (off Chromium), 2014/09/24 01:35:02]

There'll be a warning on the console for this extension that the file couldn't
be found. But since this extension is hidden from the user unless they pass
--show-component-extension-options, it shouldn't be user visible. Calling play()
appears to just do nothing.

   }
 
   /**
    * @enum {number}
    * @private
    */
   StateManager.State_ = {
     STOPPED: 0,
     STARTING: 1,
     RUNNING: 2,
@@ skipping 162 matching lines @@
 
     /**
      * Handle hotword triggering.
      * @private
      */
     onTrigger_: function() {
       assert(this.pluginManager_);
       // Detector implicitly stops when the hotword is detected.
       this.state_ = State_.STOPPED;
 
+      // Play the chime.
+      this.chime_.play();

[Dan Beam, 2014/09/23 03:43:13]

can this handle being called before the sound stops playing or if not loaded
yet?

[Anand Mistry (off Chromium), 2014/09/24 01:35:02]

The sound is shorter than 1 second. I don't think it's reasonable to try an
handle playing if it's already playing. As for not loaded, the file either
doesn't exist, which should only happen when the shared module isn't installed
and hence this code path won't be invoked, or the URL was slow to be loaded. I'm
not sure if it's worth trying to handle that.

+
       chrome.hotwordPrivate.notifyHotwordRecognition('search', function() {});
 
       // Implicitly clear the session. A session needs to be started in order to
       // restart the detector.
       this.sessionSource_ = null;
       this.sessionStartedCb_ = null;
     },
 
     /**
      * Start a hotwording session.
@@ skipping 17 matching lines @@
       this.sessionSource_ = null;
       this.sessionStartedCb_ = null;
       this.updateStateFromStatus_();
     }
   };
 
   return {
     StateManager: StateManager
   };
 });