[net] Add an informational bubble to about:net-internals#proxy when using a single SOCKS v5 proxy s…

chrome/browser/resources/net_internals/proxy_view.html

 <!-- Proxy info -->
 
 <style>
 
 #proxy-view-tab-content td,
 #proxy-view-tab-content th {
   font-size: 85%;
 }
 
+#proxy-view-socks-hints {
+  border: 1px solid orange;
+  padding: 1ex;
+}
+
+#proxy-view-socks-hints-flag {
+  margin: 1ex;
+}
+
 </style>
 
 <div id=proxy-view-tab-content class=content-box>
   <h4>
     Current proxy settings
     <input type=button value="Re-apply settings" id=proxy-view-reload-settings class="hide-when-not-capturing">
   </h4>
 
   <table><tr>
 
   <td valign=top>
   <h3>Effective settings</h3>
   <pre id=proxy-view-effective-settings></pre>
   </td>
 
   <td style='width: 30px'>&nbsp;</td>
 
   <td valign=top>
   <h3>Original settings</h3>
   <pre id=proxy-view-original-settings></pre>
   </td>
 
   </tr></table>
 
+  <div id=proxy-view-socks-hints>
+    Note that some traffic such as DNS prefetching will NOT go through the proxy
+    server. To prevent the browser from doing local DNS resolves try adding this
+    command line flag:
+    <pre id=proxy-view-socks-hints-flag></pre>
+  </div>
+
   <h4>
     Recently failed proxies, marked as bad
     <input type=button value="Clear bad proxies" id=proxy-view-clear-bad-proxies class="hide-when-not-capturing">
   </h4>
   <table class="styled-table">
     <thead>
       <tr>
         <th>Bad proxy server</th>
         <th>Time for next retry</th>
       </tr>
     </thead>
     <tbody id=proxy-view-bad-proxies-tbody></tbody>
   </table>
 </div>