Update chrome.metricsPrivate externs and make closure fixes

chrome/browser/resources/hotword/metrics.js

 // Copyright 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.metrics', function() {
   'use strict';
 
   /**
    * Helper function to record enum values in UMA.
    * @param {!string} name
    * @param {!number} value
    * @param {!number} maxValue
    */
   function recordEnum(name, value, maxValue) {
     var metricDesc = {
       'metricName': name,
-      'type': 'histogram-linear',
+      'type': chrome.metricsPrivate.MetricTypeType.HISTOGRAM_LINEAR,
       'min': 1,
       'max': maxValue,
       'buckets': maxValue + 1
     };
     chrome.metricsPrivate.recordValue(metricDesc, value);
   }
 
   return {
     recordEnum: recordEnum
   };
 });