Support USB transfers from arbitrary threads in the new Linux backend.

Support USB transfers from arbitrary threads in the new Linux backend.

DevTools relies on being able to issue USB transfers from an arbitrary
thread and have the callback run back on that thread. This is possible
in the libusb version but not the new native Linux version. This patch
adds the necessary thread hopping logic for that but only for bulk and
interrupt transfers as DevTools only uses those.

BUG=603434
Committed: https://crrev.com/6aa3211e5f2b8a4bbe400e24d448d2ceb4c60115
Cr-Commit-Position: refs/heads/master@{#390227}

[Reilly Grant (use Gerrit), 2016-04-27 21:15:55]

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

[Reilly Grant (use Gerrit), 2016-04-27 21:15:56]

Please take a look.

[juncai, 2016-04-27 22:08:59]

LGTM.

[Reilly Grant (use Gerrit), 2016-04-27 22:12:45]

The CQ bit was checked by reillyg@chromium.org

[commit-bot: I haz the power, 2016-04-27 22:13:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1916053006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1916053006/1

[commit-bot: I haz the power, 2016-04-27 23:11:46]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-04-30 17:14:16]

Patchset 1 (id:??) landed as
https://crrev.com/6aa3211e5f2b8a4bbe400e24d448d2ceb4c60115
Cr-Commit-Position: refs/heads/master@{#390227}

[commit-bot: I haz the power, 2016-04-30 17:52:40]

Description was changed from

==========
Support USB transfers from arbitrary threads in the new Linux backend.

DevTools relies on being able to issue USB transfers from an arbitrary
thread and have the callback run back on that thread. This is possible
in the libusb version but not the new native Linux version. This patch
adds the necessary thread hopping logic for that but only for bulk and
interrupt transfers as DevTools only uses those.

BUG=603434
==========

to

==========
Support USB transfers from arbitrary threads in the new Linux backend.

DevTools relies on being able to issue USB transfers from an arbitrary
thread and have the callback run back on that thread. This is possible
in the libusb version but not the new native Linux version. This patch
adds the necessary thread hopping logic for that but only for bulk and
interrupt transfers as DevTools only uses those.

BUG=603434

Committed: https://crrev.com/6aa3211e5f2b8a4bbe400e24d448d2ceb4c60115
Cr-Commit-Position: refs/heads/master@{#390227}
==========