Settings: Internet: Update proxy controlled indicator and fields.

chrome/browser/resources/settings/internet_page/network_proxy_exclusions.html

 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="internet_shared_css.html">
 
 <dom-module id="network-proxy-exclusions">
   <template>
     <style include="internet-shared">
       iron-icon {
         @apply(--settings-actionable);
         margin: 5px;
       }
 
       #container {
         align-self: stretch;
         border: 1px solid lightgrey;
         height: 100px;
         margin-top: 10px;
         overflow-y: auto;
         padding: 5px;
       }
     </style>
     <div id="container">
       <template is="dom-repeat" items="[[exclusions]]">
         <div class="layout horizontal center" tabindex="0" >
           <div class="flex">[[item]]</div>
           <iron-icon class="favicon-image" icon="cr:clear"
-              on-tap="onRemoveTap_" tabindex="0">
+              on-tap="onRemoveTap_" tabindex="0" hidden="[[!editable]]">
           </iron-icon>
         </div>
       </template>
     </div>
   </template>
   <script src="network_proxy_exclusions.js"></script>
 </dom-module>