Added auto-scan, made some small changes to how prefs are stored, refactored.

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

Index: chrome/browser/resources/chromeos/switch_access/options.js
diff --git a/chrome/browser/resources/chromeos/switch_access/options.js b/chrome/browser/resources/chromeos/switch_access/options.js
index 9d59dd6e1b611e29d27957bbfe9a19d3589334f1..a0fc85fe597b8c59cfacab703d1706f37dabbf10 100644
--- a/chrome/browser/resources/chromeos/switch_access/options.js
+++ b/chrome/browser/resources/chromeos/switch_access/options.js
@@ -41,9 +41,9 @@ SwitchAccessOptions.prototype = {
    * @private
    */
   init_: function() {
-    let prefs = this.switchAccessPrefs_.getPrefs();
-    $('enableAutoScan').checked = prefs['enableAutoScan'];
-    $('autoScanTime').value = prefs['autoScanTime'];
+    $('enableAutoScan').checked =
+        this.switchAccessPrefs_.getPref('enableAutoScan');
+    $('autoScanTime').value = this.switchAccessPrefs_.getPref('autoScanTime');
   },
 
   /**
@@ -53,17 +53,40 @@ SwitchAccessOptions.prototype = {
    * @private
    */
   handleInputChange_: function(event) {
-    switch (event.target.id) {
+    let input = event.target;
+    switch (input.id) {
       case 'enableAutoScan':
-        this.switchAccessPrefs_.setPref(event.target.id, event.target.checked);
+        this.switchAccessPrefs_.setPref(input.id, input.checked);
         break;
       case 'autoScanTime':
-        this.switchAccessPrefs_.setPref(event.target.id, event.target.value);
+        let oldVal =
+            /** @type {number} */ (this.switchAccessPrefs_.getPref(input.id));
+        let val = Number(input.value);
+        let min = Number(input.min);
+        if (this.isValidInput_(val, oldVal, min)) {
+          input.value = val;
+          this.switchAccessPrefs_.setPref(input.id, val);
+        } else {
+          input.value = oldVal;
+        }
         break;
     }
   },
 
   /**
+   * Return true if the input is a valid autoScanTime input. Otherwise, return
+   * false.
+   *
+   * @param {number} value
+   * @param {number} oldValue
+   * @param {number} min
+   * @return {boolean}
+   */
+  isValidInput_: function(value, oldValue, min) {
+    return (value !== oldValue) && (value >= min);
+  },
+
+  /**
    * Handle a change in user preferences.
    *
    * @param {!Event} event