Open HID connections asynchronously.

Open HID connections asynchronously.

By making HidService::Connect return its result asynchronously platform
specific details such as whether device nodes must be opened on a
different thread (due to blocking) or requesting access from the Chrome
OS permission broker can be abstracted away.

BUG=422540
Committed: https://crrev.com/7f4f508547ac3058d7c47337313972ec1ac2fb1b
Cr-Commit-Position: refs/heads/master@{#299950}

[Reilly Grant (use Gerrit), 2014-10-15 22:54:09]

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

[Reilly Grant (use Gerrit), 2014-10-15 23:52:17]

Please take a look.

[rpaquay, 2014-10-16 18:03:31]

lgtm

[Reilly Grant (use Gerrit), 2014-10-16 18:06:05]

The CQ bit was checked by reillyg@chromium.org

[commit-bot: I haz the power, 2014-10-16 18:07:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/660573007/1

[commit-bot: I haz the power, 2014-10-16 19:19:32]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-16 19:22:30]

Patchset 1 (id:??) landed as
https://crrev.com/7f4f508547ac3058d7c47337313972ec1ac2fb1b
Cr-Commit-Position: refs/heads/master@{#299950}