DevTools: Extract target discovery and manipulation from DevToolsHttpHandlerImpl

chrome/test/data/devtools/target_list/background.js

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 function requestUrl(url, callback) {
   var req = new XMLHttpRequest();
   req.open('GET', url, true);
   req.onload = function() {
     if (req.status == 200)
       callback(req.responseText);
@@ skipping 16 matching lines @@
 
   var wsAddress = REMOTE_DEBUGGER_HOST + '/devtools/page/' + target.id;
 
   chrome.test.assertEq(
       '/devtools/devtools.html?ws=' + wsAddress,
       target.devtoolsFrontendUrl);
   // On some platforms (e.g. Chrome OS) target.faviconUrl might be empty for
   // a freshly created tab. Ignore the check then.
   if (target.faviconUrl)
     chrome.test.assertEq(opt_faviconUrl, target.faviconUrl);
-  chrome.test.assertEq('/thumb/' + target.id, target.thumbnailUrl);
+  // Sometimes thumbnailUrl is not available for a freshly loaded tab.
+  if (target.thumbnailUrl)
+    chrome.test.assertEq('/thumb/' + target.id, target.thumbnailUrl);
   chrome.test.assertEq(opt_title || target.url, target.title);
   chrome.test.assertEq(type, target.type);
   chrome.test.assertEq('ws://' + wsAddress, target.webSocketDebuggerUrl);
 }
 
 chrome.test.runTests([
   function discoverTargets() {
     var testPageUrl = chrome.extension.getURL('test_page.html');
 
     function onUpdated() {
       chrome.tabs.onUpdated.removeListener(onUpdated);
       requestUrl('http://' + REMOTE_DEBUGGER_HOST + '/json', function(text) {
         var targets = JSON.parse(text);
 
         checkTarget(targets, 'about:blank', 'page');
         checkTarget(targets, testPageUrl, 'page', 'Test page',
             chrome.extension.getURL('favicon.png'));
         checkTarget(targets,
             chrome.extension.getURL('_generated_background_page.html'),
             'other');
 
         chrome.test.succeed();
       });
     }
     chrome.tabs.onUpdated.addListener(onUpdated);
     chrome.tabs.create({url: testPageUrl});
   }
 ]);