Fix CrOS FileManagerBrowserTest with scheduler enabled

Fix CrOS FileManagerBrowserTest with scheduler enabled

The timeouts in OpenAudioFiles/FileManagerBrowserTest where
due to a task reordering which caused
audioPlayerApp.closeWindowAndWait to never complete because
the call to getWindows failed silently.

Patches 837203002 and 832183008 must be submitted first.

BUG=432129, 444574
Committed: https://crrev.com/e19d4ef3a1fd8d287ea198b1bf37241d2046a1cc
Cr-Commit-Position: refs/heads/master@{#310791}

[alex clarke (OOO till 29th), 2015-01-08 10:34:22]

alexclarke@chromium.org changed reviewers:
+ skyostil@chromium.org

[alex clarke (OOO till 29th), 2015-01-08 10:34:45]

alexclarke@chromium.org changed reviewers:
+ jochen@chromium.org

[alex clarke (OOO till 29th), 2015-01-08 10:59:50]

alexclarke@chromium.org changed reviewers:
+ rmcilroy@chromium.org

[Sami, 2015-01-08 11:33:31]

lgtm once the other patches are in.

[jochen (gone - plz use gerrit), 2015-01-08 13:11:36]

lgtm

[alex clarke (OOO till 29th), 2015-01-09 10:28:29]

The CQ bit was checked by alexclarke@chromium.org

[commit-bot: I haz the power, 2015-01-09 10:28:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/838193002/1

[alex clarke (OOO till 29th), 2015-01-09 11:21:20]

The CQ bit was unchecked by alexclarke@chromium.org

[alex clarke (OOO till 29th), 2015-01-09 11:58:53]

I had to change MockRenderThread::GetTaskRunner since this patch was failing on
some bots.

[Sami, 2015-01-09 12:27:48]

lgtm.

[alex clarke (OOO till 29th), 2015-01-09 12:29:03]

The CQ bit was checked by alexclarke@chromium.org

[commit-bot: I haz the power, 2015-01-09 12:30:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/838193002/20001

[commit-bot: I haz the power, 2015-01-09 13:55:10]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-01-09 13:55:11]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel_ng on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[alex clarke (OOO till 29th), 2015-01-09 14:54:38]

As discussed offline (with Sami) I've reduced the scope of this patch.  it just
fixes the CrOS FileManagerBrowserTest.  I'll separately fix the
SpokenFeedbackTest.

[alex clarke (OOO till 29th), 2015-01-09 14:55:14]

The CQ bit was checked by alexclarke@chromium.org

[commit-bot: I haz the power, 2015-01-09 14:55:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/838193002/60001

[commit-bot: I haz the power, 2015-01-09 16:36:48]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-01-09 16:36:49]

Try jobs failed on following builders:
  android_dbg_tests_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_dbg_tes...)

[alex clarke (OOO till 29th), 2015-01-09 16:57:00]

The CQ bit was checked by alexclarke@chromium.org

[commit-bot: I haz the power, 2015-01-09 16:57:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/838193002/80001

[commit-bot: I haz the power, 2015-01-09 17:46:09]

Committed patchset #5 (id:80001)

[commit-bot: I haz the power, 2015-01-09 17:46:57]

Patchset 5 (id:??) landed as
https://crrev.com/e19d4ef3a1fd8d287ea198b1bf37241d2046a1cc
Cr-Commit-Position: refs/heads/master@{#310791}