Misc clean-up of TabCaptureApiTests; and re-enable more tests.

chrome/test/data/extensions/api_test/tab_capture/api_tests.js

 // Copyright 2014 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.
 
 var tabCapture = chrome.tabCapture;
 
 chrome.test.runTests([
   function captureTabAndVerifyStateTransitions() {
     // Tab capture events in the order they happen.
     var tabCaptureEvents = [];
@@ skipping 27 matching lines @@
           if (infos[i].tabId == secondTab) {
             chrome.test.assertNe(null, status);
             chrome.test.assertEq(status, infos[i].status);
             chrome.test.assertEq(false, infos[i].fullscreen);
             return;
           }
         }
       }
 
       // Step 4: After the second tab is closed, check that getCapturedTabs()
-      // returns no info at all about the second tab.  http://crbug.com/338445
+      // returns no info at all about the second tab.
       chrome.tabs.onRemoved.addListener(function() {
         tabCapture.getCapturedTabs(function checkNoInfos(infos) {
           checkInfoForSecondTabHasStatus(infos, null);
           chrome.test.succeed();
         });
       });
 
       var activeStream = null;
 
       // Step 3: After the stream is stopped, check that getCapturedTabs()
@@ skipping 39 matching lines @@
   },
 
   function onlyVideo() {
     tabCapture.capture({video: true}, function(stream) {
       chrome.test.assertTrue(!!stream);
       stream.stop();
       chrome.test.succeed();
     });
   },
 
+  function onlyAudio() {
+    tabCapture.capture({audio: true}, function(stream) {
+      chrome.test.assertTrue(!!stream);
+      stream.stop();
+      chrome.test.succeed();
+    });
+  },
+
   function noAudioOrVideoRequested() {
     // If not specified, video is not requested.
     tabCapture.capture({audio: false}, function(stream) {
       chrome.test.assertTrue(!stream);
       chrome.test.succeed();
     });
   }
-
 ]);