Added to options page to let users change keyboard mappings.

chrome/browser/resources/chromeos/switch_access/prefs.js

 // Copyright 2017 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.
 
 /**
  * Class to manage user preferences.
  *
  * @constructor
  */
 function SwitchAccessPrefs() {
   /**
    * User preferences, initially set to the default preference values.
    *
    * @private
    */
-  this.prefs_ = Object.assign({}, this.DEFAULT_PREFS);
+  this.prefs_ = Object.assign(
+      {}, this.DEFAULT_COMMAND_KEYCODE_MAP, this.DEFAULT_OTHER_PREFS);
 
   this.loadPrefs_();
   chrome.storage.onChanged.addListener(this.handleStorageChange_.bind(this));
 }
 
 SwitchAccessPrefs.prototype = {
   /**
    * Asynchronously load the current preferences from chrome.storage.sync and
    * store them in this.prefs_, if this.prefs_ is not already set to that value.
    * If this.prefs_ changes, fire a prefsUpdate event.
    *
    * @private
    */
   loadPrefs_: function() {
-    let defaultKeys = Object.keys(this.DEFAULT_PREFS);
+    let defaultKeys = Object.keys(this.prefs_);
     chrome.storage.sync.get(defaultKeys, function(loadedPrefs) {
       let updatedPrefs = {};
       for (let key of Object.keys(loadedPrefs)) {
         if (this.prefs_[key] !== loadedPrefs[key]) {
           this.prefs_[key] = loadedPrefs[key];
           updatedPrefs[key] = loadedPrefs[key];
         }
       }
       if (Object.keys(updatedPrefs).length > 0) {
         let event = new CustomEvent('prefsUpdate', {'detail': updatedPrefs});
@@ skipping 77 matching lines @@
    */
   getStringPref: function(key) {
     let value = this.prefs_[key];
     if (typeof value === 'string')
       return value;
     else
       throw new TypeError('No value of string type for key \'' + key + '\'');
   },
 
   /**
-   * The default value of all preferences. All preferences should be primitives
-   * to prevent changes to default values.
+   * Get a list of the commands that can be run using a keyboard key.
+   *
+   * @return {!Array<string>}
+   */
+  getCommands: function() {
+    return Object.keys(this.DEFAULT_COMMAND_KEYCODE_MAP);
+  },
+
+  /**
+   * Returns true if |keyCode| is already used to run a command from the
+   * keyboard.
+   *
+   * @param {number} keyCode
+   * @return {boolean}
+   */
+  keyCodeIsUsed: function(keyCode) {
+    for (let command of this.getCommands()) {
+      if (keyCode === this.prefs_[command])
+        return true;
+    }
+    return false;
+  },
+
+  /**
+   * The default mapping between commands and key codes.
    *
    * @const
    */
-  DEFAULT_PREFS: {
+  DEFAULT_COMMAND_KEYCODE_MAP: {
+    'next': 49,
+    'previous': 50,
+    'select': 51,
+    'options': 52,
+    'debugNext': 54,
+    'debugPrevious': 55,
+    'debugChild': 56,
+    'debugParent': 57
+  },
+
+  /**
+   * The default value of all other preferences. All preferences should be
+   * primitives to prevent changes to default values.
+   *
+   * @const
+   */
+  DEFAULT_OTHER_PREFS: {
     'enableAutoScan': false,
     'autoScanTime': 800
   }
 };