[MD Extensions] Add the source type on the details page for an extension

chrome/browser/resources/md_extensions/detail_view.html

 <link rel="import" href="chrome://resources/html/cr.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout-classes.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/iron-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-checkbox/paper-checkbox.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animatable-behavior.html">
 <link rel="import" href="chrome://extensions/animation_helper.html">
+<link rel="import" href="chrome://extensions/item_source.html">
 
 <dom-module id="extensions-detail-view">
   <style include="iron-flex"></style>
   <template>
     <style>
       #main {
         background-color: white;
         height: 800px;
         width: 90%;
       }
@@ skipping 108 matching lines @@
             <paper-checkbox id="collect-errors" class="checkbox"
                 checked="[[data.errorCollection.isActive]]"
                 on-change="onCollectErrorsChange_">
               $i18n{itemCollectErrors}
             </paper-checkbox>
           </template>
         </div>
       </template>
       <div class="section">
         <div class="section-title">$i18n{itemSource}</div>
-        <div class="section-content">TODO</div>
+        <div class="section-content">
+          [[computeSourceString_(data.*)]]
+        </div>
       </div>
     </div>
   </template>
   <script src="chrome://extensions/detail_view.js"></script>
 </dom-module>