[Android] Use the UI thread for VSyncMonitorTest vsync requests

[Android] Use the UI thread for VSyncMonitorTest vsync requests

VSyncMonitor is not thread-safe, and is not intended to be. When a vsync
request is made from a non-UI thread, there is a race where both a
synthetic and frame-based callback can fire for the same request. Avoid
this by making sure VSyncMonitorTest only requests updates from the UI
thread, representative of production code behavior.

BUG=498007
Committed: https://crrev.com/aab443b709be482b746ffa47c3a04e69fade3e83
Cr-Commit-Position: refs/heads/master@{#333580}

[jdduke (slow), 2015-06-09 01:26:27]

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

[jdduke (slow), 2015-06-09 01:26:28]

skyostil@: PTAL, should have caught this sooner.

[Sami, 2015-06-09 12:57:31]

Thanks for catching this -- lgtm.

I guess we can find small comfort in the fact that this wasn't happening in
production code. Threading is hard.

[jdduke (slow), 2015-06-09 15:14:53]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2015-06-09 15:15:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1166223003/1

[commit-bot: I haz the power, 2015-06-09 17:32:24]

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

[commit-bot: I haz the power, 2015-06-09 17:32:25]

Try jobs failed on following builders:
  linux_android_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_android_r...)

[jdduke (slow), 2015-06-09 21:06:16]

The CQ bit was checked by jdduke@chromium.org

[jdduke (slow), 2015-06-09 21:06:17]

The patchset sent to the CQ was uploaded after l-g-t-m from
skyostil@chromium.org
Link to the patchset: https://codereview.chromium.org/1166223003/#ps20001
(title: "Fix test")

[commit-bot: I haz the power, 2015-06-09 21:08:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1166223003/20001

[commit-bot: I haz the power, 2015-06-09 21:51:23]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-06-09 21:52:04]

Patchset 2 (id:??) landed as
https://crrev.com/aab443b709be482b746ffa47c3a04e69fade3e83
Cr-Commit-Position: refs/heads/master@{#333580}

[mithro-old, 2015-06-23 09:14:57]

Late LGTM. 

Thanks for adding the asserts.