Implement debugging local unlock keys in chrome://proximity-auth.

components/proximity_auth/webui/resources/log-panel.html

 <link href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout.html" rel="import">
 <link href="chrome://resources/polymer/v1_0/iron-icons/communication-icons.html" rel="import">
 <link href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html" rel="import">
 <link href="chrome://resources/polymer/v1_0/paper-toolbar/paper-toolbar.html" rel="import">
 <link href="chrome://resources/polymer/v1_0/polymer/polymer.html" rel="import">
 <link href="log-buffer.html" rel="import">
 
 <dom-module id="log-panel">
   <style>
     :host {
@@ skipping 52 matching lines @@
 
   <template>
     <paper-toolbar class="layout horizontal end-justified center"
                   on-click="clearLogs_">
       <paper-icon-button icon="communication:clear-all"></paper-icon-button>
     </paper-toolbar>
 
     <log-buffer id='logBuffer' logs="{{logs}}"></log-buffer>
     <div id="list" class="flex">
       <template is="dom-repeat" items="[[logs]]">
-        <div class="list-item" severity="[[item.severity]]">
+        <div class="list-item" severity$="[[item.severity]]">
           <div class="item-metadata layout horizontal">
             <div>[[item.time]]</div>
             <div class="flex"></div>
             <div>[[computeFileAndLine_(item)]]</div>
           </div>
           <pre class="item-log flex">[[item.text]]</pre>
         </div>
       </template>
     </div>
   </template>
   <script src="log-panel.js"></script>
 </dom-module>