Update Stats element to use new directory layout

appengine/swarming/elements/res/imp/stats/load-charts-api.html

 <!--
 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed by the Apache v2.0 license that can be
 # found in the LICENSE file.
 -->
 <!--
   This in an HTML Import-able file that contains the definition
   of the following elements:
 
     <load-charts-api>
@@ skipping 11 matching lines @@
     loaded: Boolean, true if the charts api has been loaded.
 
   Methods:
     None.
 
   Events:
     None.
 -->
 
 <script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>
-<link rel="import" href="/imp/bower_components/google-apis/google-legacy-loader.html">
+<link rel="import" href="/res/imp/bower_components/google-apis/google-legacy-loader.html">
 
 <dom-module id="load-charts-api">
   <template>
 
     <google-legacy-loader on-api-load="_readyForAction"></google-legacy-loader>
 
   </template>
   <script>
     Polymer({
       is: 'load-charts-api',
       properties: {
         loaded: {
           type: Boolean,
           notify: true,
         }
       },
 
       _readyForAction: function() {
         google.load("visualization", "1", {
           packages: {packages: ['corechart']},
           callback: function() {
             this.set("loaded", true);
           }.bind(this)
         });
       }
     });
   </script>
 </dom-module>