Move device opening from DeviceManager to Device.

Move device opening from DeviceManager to Device.

This makes the Device::GetConfiguration method callable even if the
device is not open (which is good) and makes the Mojo interface closer
to the WebUSB API.

Committed: https://crrev.com/47fc2064019a963683a0682237c0ac58f754f713
Cr-Commit-Position: refs/heads/master@{#349968}

[Reilly Grant (use Gerrit), 2015-09-18 20:42:51]

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

[Reilly Grant (use Gerrit), 2015-09-18 20:42:52]

Please take a look. I like how this cleaned up the split between
WebUSBClientImpl and WebUSBDeviceImpl.

[Ken Rockot(use gerrit already), 2015-09-21 16:51:21]

lgtm

[Reilly Grant (use Gerrit), 2015-09-21 17:11:04]

The CQ bit was checked by reillyg@chromium.org

[commit-bot: I haz the power, 2015-09-21 17:11:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1352683006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1352683006/1

[commit-bot: I haz the power, 2015-09-21 18:28:28]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-21 18:29:46]

Patchset 1 (id:??) landed as
https://crrev.com/47fc2064019a963683a0682237c0ac58f754f713
Cr-Commit-Position: refs/heads/master@{#349968}