Observe UsbService from the FILE thread in DevicePermissionsManager.

Observe UsbService from the FILE thread in DevicePermissionsManager.

As in the UsbEventRouter the UsbService must be observed from the FILE
thread (until bug 427985 is resolved, which will be soon). This change
fixes a DCHECK(CalledOnValidThread()) in UsbService::AddObserver when
permission to access an ephemeral (no serial number) device is added and
the DevicePermissionsManager starts listening for disconnection of that
device.

BUG=452652
Committed: https://crrev.com/897bbc219ac773a8a6c5799bc323b9fa8eea0989
Cr-Commit-Position: refs/heads/master@{#313548}

[Reilly Grant (use Gerrit), 2015-01-27 21:57:32]

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

[Reilly Grant (use Gerrit), 2015-01-27 22:02:41]

Patchset #1 (id:1) has been deleted

[Reilly Grant (use Gerrit), 2015-01-27 23:06:34]

Patchset #1 (id:20001) has been deleted

[Reilly Grant (use Gerrit), 2015-01-27 23:45:13]

Vince, please take a look at this patch. I'm going to have to merge it to M-41
because of the threading issue it fixes.

[scheib, 2015-01-27 23:56:25]

https://codereview.chromium.org/882813002/diff/40001/extensions/browser/api/d...
File extensions/browser/api/device_permissions_manager.cc (right):

https://codereview.chromium.org/882813002/diff/40001/extensions/browser/api/d...
extensions/browser/api/device_permissions_manager.cc:412:
base::TimeDelta::FromMinutes(5));
ಠ_ಠ

[Reilly Grant (use Gerrit), 2015-01-28 01:00:22]

On 2015/01/27 23:56:25, scheib wrote:
>
https://codereview.chromium.org/882813002/diff/40001/extensions/browser/api/d...
> File extensions/browser/api/device_permissions_manager.cc (right):
> 
>
https://codereview.chromium.org/882813002/diff/40001/extensions/browser/api/d...
> extensions/browser/api/device_permissions_manager.cc:412:
> base::TimeDelta::FromMinutes(5));
> ಠ_ಠ

I've removed this part of the fix. This patch will resolve the threading issue
only. I have a better solution for tracking UsbDevice lifetime but it requires
more code so I will submit it separately.

[scheib, 2015-01-28 18:32:33]

lgtm

[Reilly Grant (use Gerrit), 2015-01-28 18:42:41]

The CQ bit was checked by reillyg@chromium.org

[commit-bot: I haz the power, 2015-01-28 18:45:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/882813002/60001

[commit-bot: I haz the power, 2015-01-28 18:48:18]

Committed patchset #2 (id:60001)

[commit-bot: I haz the power, 2015-01-28 18:49:11]

Patchset 2 (id:??) landed as
https://crrev.com/897bbc219ac773a8a6c5799bc323b9fa8eea0989
Cr-Commit-Position: refs/heads/master@{#313548}