Manage UsbService lifetime in DeviceClient implementations.

Manage UsbService lifetime in DeviceClient implementations.

To make it easier to reason about when the UsbService is destroyed this
patch makes its lifetime managed by the DeviceClient implementation that
created it. This means that in Chrome the UsbService is (indirectly)
owned by BrowserProcessImpl.

BUG=None
TBR=dgozman@chromium.org

Committed: https://crrev.com/badbc5415c4cd4d4870b2ca2122b1b9988e341d7
Cr-Commit-Position: refs/heads/master@{#346264}

[Reilly Grant (use Gerrit), 2015-08-28 19:49:47]

Patchset #1 (id:1) has been deleted

[Reilly Grant (use Gerrit), 2015-08-28 19:49:53]

Patchset #1 (id:20001) has been deleted

[Reilly Grant (use Gerrit), 2015-08-28 19:50:03]

Patchset #1 (id:40001) has been deleted

[Reilly Grant (use Gerrit), 2015-08-28 19:50:12]

Patchset #1 (id:60001) has been deleted

[Reilly Grant (use Gerrit), 2015-08-28 19:50:21]

Patchset #1 (id:80001) has been deleted

[Reilly Grant (use Gerrit), 2015-08-28 20:21:50]

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

[Reilly Grant (use Gerrit), 2015-08-28 20:21:51]

Please take a look. I've finally drunk the globals are evil koolaid.

[Ken Rockot(use gerrit already), 2015-08-28 22:54:13]

and lgtm

[Reilly Grant (use Gerrit), 2015-08-28 22:54:40]

The CQ bit was checked by reillyg@chromium.org

[Reilly Grant (use Gerrit), 2015-08-28 22:54:44]

The CQ bit was unchecked by reillyg@chromium.org

[Reilly Grant (use Gerrit), 2015-08-28 22:55:27]

The CQ bit was checked by reillyg@chromium.org

[commit-bot: I haz the power, 2015-08-28 22:56:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1314273002/100001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1314273002/100001

[commit-bot: I haz the power, 2015-08-28 23:08:18]

Committed patchset #1 (id:100001)

[commit-bot: I haz the power, 2015-08-28 23:08:52]

Patchset 1 (id:??) landed as
https://crrev.com/badbc5415c4cd4d4870b2ca2122b1b9988e341d7
Cr-Commit-Position: refs/heads/master@{#346264}