Enable USB gadget tests on OS X.

Enable USB gadget tests on OS X.

This change fixes the USB device handle tests on OS X by claiming the
necessary interfaces before using them and using the right endpoint
numbers. It also enables the HID connection tests on OS X by creating
a MessageLoopForUI on the main thread (to mimic the usual configuration
in the Chrome browser process) and a separate thread running a
MessageLoopForIO.

Committed: https://crrev.com/67650d64ea56326fef63e5d9812b6fd2590a2a25
Cr-Commit-Position: refs/heads/master@{#308210}

[Reilly Grant (use Gerrit), 2014-12-12 22:33:02]

reillyg@chromium.org changed reviewers:
+ rockot@chromium.org

[Reilly Grant (use Gerrit), 2014-12-12 22:33:25]

Patchset #1 (id:1) has been deleted

[Reilly Grant (use Gerrit), 2014-12-12 23:43:17]

Patchset #1 (id:20001) has been deleted

[Reilly Grant (use Gerrit), 2014-12-13 00:04:29]

Ken, please take a look. I'm working on getting this working on Windows too but
this is a good checkpoint.

[Ken Rockot(use gerrit already), 2014-12-13 00:23:07]

lgtm

[Reilly Grant (use Gerrit), 2014-12-13 00:36:14]

The CQ bit was checked by reillyg@chromium.org

[commit-bot: I haz the power, 2014-12-13 00:37:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/804643002/40001

[commit-bot: I haz the power, 2014-12-13 01:19:00]

Committed patchset #1 (id:40001)

[commit-bot: I haz the power, 2014-12-13 01:19:58]

Patchset 1 (id:??) landed as
https://crrev.com/67650d64ea56326fef63e5d9812b6fd2590a2a25
Cr-Commit-Position: refs/heads/master@{#308210}