Added to options page to let users change keyboard mappings.

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

Index: chrome/browser/resources/chromeos/switch_access/prefs.js
diff --git a/chrome/browser/resources/chromeos/switch_access/prefs.js b/chrome/browser/resources/chromeos/switch_access/prefs.js
index 15ae9dd93f15c24e56ad68428bb157850a4b1504..9be570a7723b16a10dab0b1f5ff5ade579a37b2c 100644
--- a/chrome/browser/resources/chromeos/switch_access/prefs.js
+++ b/chrome/browser/resources/chromeos/switch_access/prefs.js
@@ -13,7 +13,8 @@ function SwitchAccessPrefs() {
    *
    * @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));
@@ -28,7 +29,7 @@ SwitchAccessPrefs.prototype = {
    * @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)) {
@@ -126,12 +127,52 @@ SwitchAccessPrefs.prototype = {
   },
 
   /**
-   * 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_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_PREFS: {
+  DEFAULT_OTHER_PREFS: {
     'enableAutoScan': false,
     'autoScanTime': 800
   }