Fix devtools documentation issue.

chrome/common/extensions/docs/templates/articles/devtools.html

 <h1>Extending DevTools</h1>
 
 <h2 id="overview">Overview</h2>
 
 <p>A DevTools extension adds functionality to the Chrome DevTools. It can add new
 UI panels and sidebars, interact with the inspected page, get information about
 network requests, and more. View <a href="https://developer.chrome.com/devtools/docs/extensions-gallery">featured DevTools extensions</a>. DevTools extensions have access to an additional set
 of DevTools-specific extension APIs:</p>
 
 <ul>
@@ skipping 191 matching lines @@
 chrome.runtime.onConnect.addListener(function(devToolsConnection) {
     // assign the listener function to a variable so we can remove it later
     var devToolsListener = function(message, sender, sendResponse) {
         // Inject a content script into the identified tab
         chrome.tabs.executeScript(message.tabId,
             { file: message.scriptToInject });
     }
     // add the listener
     devToolsConnection.onMessage.addListener(devToolsListener);
 
-    devToolsConnection.onDisconnect(function() {
+    devToolsConnection.onDisconnect.addListener(function() {
          devToolsConnection.onMessage.removeListener(devToolsListener);
     });
 }
 </pre>
 
 <h3 id="evaluating-js">Evaluating JavaScript in the Inspected Window</h3>
 
 <p>You can use the <code>$(ref:inspectedWindow.eval)</code> method to execute
 JavaScript code in the context of the inspected page. You can invoke the
 <code>eval</code> method from a DevTools page, panel or sidebar pane.</p>
@@ skipping 275 matching lines @@
 <p>
 <a href="http://groups.google.com/group/google-chrome-developer-tools/topics">Give
 us feedback!</a>
 Your comments and suggestions help us improve the APIs.</p>
 
 <h2 id="examples">Examples</h2>
 
 <p>You can find examples that use DevTools APIs in
 <a href="http://developer.chrome.com/extensions/samples.html#devtools">Samples</a>.
 </p>