getUserMedia: handle the device starting status report.

chrome/test/data/extensions/api_test/desktop_capture/test.js

 // Copyright 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 onPickerResult(audio_track_num, id, options) {
   chrome.test.assertEq("string", typeof id);
   chrome.test.assertTrue(id != "");
   var video_constraint = { mandatory: { chromeMediaSource: "desktop",
                                         chromeMediaSourceId: id } };
   var audio_constraint =
@@ skipping 105 matching lines @@
 
   function cancelDialog() {
     var requestId = chrome.desktopCapture.chooseDesktopMedia(
         ["screen", "window"],
         chrome.test.fail);
     chrome.test.assertEq("number", typeof requestId);
     chrome.desktopCapture.cancelChooseDesktopMedia(requestId);
     chrome.test.succeed();
   },
 
-  // For the following six, they all request audio track. Based on user's
-  // permission and the source type, it may or may not actually get the audio
-  // track.
-  // In detail:
-  //  1. We cannot support audio for Window share;
-  //  2. We can support audio for Tab share;
-  //  3. We can support audio for Screen share on Windows;
-  //  4. We can support audio for Screen Share on ChromeOS if USE_CRAS is on;
-  //  5. To actually get audio track, user permission is always necessary;
-  //  6. To actually get audio track, getUserMedia() should set audio
-  //     constraint.
-  function tabShareWithAudioPermissionGetStream() {
-    chrome.desktopCapture.chooseDesktopMedia(
-        ["tab", "audio"], onPickerResult.bind(undefined, 1));
-  },
-
-  function windowShareWithAudioPermissionGetStream() {
-    chrome.desktopCapture.chooseDesktopMedia(
-        ["window", "audio"], onPickerResult.bind(undefined, 0));
-  },
-
+  // Only screenShare can be tested as below, because we can't get stream with
+  // fake web-content/window source id.

[chfremer, 2017/03/02 17:56:10]

I don't immediately see why the changes in this CL make these existing test
cases impossible/obsolete.

[braveyao, 2017/03/03 17:53:12]

Revised the comments a bit. Is it better?

[chfremer, 2017/03/03 19:08:33]

The extra information in the new comment seems helpful, so definitely better.
But I still don't understand why the change in this CL causes tests that worked
before to no longer work. Isn't the only change that the response to
getUserMedia and chooseDesktopMedia now arrives a bit later than before?

[braveyao, 2017/03/03 21:34:55]

Before this cl, gUM always get successful callback, no matter device-start
succeeds or fails.
After this cl, gUM will get real device-start result through success-callback or
error-callback.
Because of the fake source id, we can't successfully create stream of tab/windwo
capture. So the removed cases will fail. And updated the cl description about
this.

   function screenShareWithAudioPermissionGetStream() {
     chrome.desktopCapture.chooseDesktopMedia(
         ["screen", "audio"],
         onPickerResult.bind(undefined,
                             expected_audio_tracks_for_screen_share));
   },
 
-  function tabShareWithoutAudioPermissionGetStream() {
-    chrome.desktopCapture.chooseDesktopMedia(
-        ["tab", "audio"], onPickerResult.bind(undefined, 0));
-  },
-
-  function windowShareWithoutAudioPermissionGetStream() {
-    chrome.desktopCapture.chooseDesktopMedia(
-        ["window", "audio"], onPickerResult.bind(undefined, 0));
-  },
-
   function screenShareWithoutAudioPermissionGetStream() {
     chrome.desktopCapture.chooseDesktopMedia(
         ["screen", "audio"], onPickerResult.bind(undefined, 0));
   }
 ]);