Implement WebUSBClient::setObserver in WebUSBClientImpl.

Implement WebUSBClient::setObserver in WebUSBClientImpl.

This patch updates WebUSBClientImpl to use the new Mojo
DeviceManager::GetDeviceChanges interface to send USB device connection
events to the observer provided by Blink.

BUG=492204
Committed: https://crrev.com/181022b6787c55ef0da34d9644eaa87b5b8d8f3c
Cr-Commit-Position: refs/heads/master@{#349137}

[Reilly Grant (use Gerrit), 2015-09-15 17:41:44]

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

[Ken Rockot(use gerrit already), 2015-09-15 18:23:34]

lgtm

https://codereview.chromium.org/1331383005/diff/1/content/renderer/usb/web_us...
File content/renderer/usb/web_usb_client_impl.cc (right):

https://codereview.chromium.org/1331383005/diff/1/content/renderer/usb/web_us...
content/renderer/usb/web_usb_client_impl.cc:115: if (observer_) {
minor nit: just return if !observer_? less whitespace for everyone!

[Reilly Grant (use Gerrit), 2015-09-15 19:49:54]

https://codereview.chromium.org/1331383005/diff/1/content/renderer/usb/web_us...
File content/renderer/usb/web_usb_client_impl.cc (right):

https://codereview.chromium.org/1331383005/diff/1/content/renderer/usb/web_us...
content/renderer/usb/web_usb_client_impl.cc:115: if (observer_) {
On 2015/09/15 18:23:34, Ken Rockot wrote:
> minor nit: just return if !observer_? less whitespace for everyone!

Done.

[Reilly Grant (use Gerrit), 2015-09-16 04:37:07]

The CQ bit was checked by reillyg@chromium.org

[Reilly Grant (use Gerrit), 2015-09-16 04:37:07]

The patchset sent to the CQ was uploaded after l-g-t-m from rockot@chromium.org
Link to the patchset: https://codereview.chromium.org/1331383005/#ps20001
(title: "Less whitespace.")

[commit-bot: I haz the power, 2015-09-16 04:37:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1331383005/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1331383005/20001

[commit-bot: I haz the power, 2015-09-16 07:57:19]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-16 07:57:20]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[Ken Rockot(use gerrit already), 2015-09-16 15:41:37]

The CQ bit was checked by rockot@chromium.org

[commit-bot: I haz the power, 2015-09-16 15:42:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1331383005/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1331383005/20001

[commit-bot: I haz the power, 2015-09-16 16:13:53]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-09-16 16:14:48]

Patchset 2 (id:??) landed as
https://crrev.com/181022b6787c55ef0da34d9644eaa87b5b8d8f3c
Cr-Commit-Position: refs/heads/master@{#349137}

[commit-bot: I haz the power, 2015-09-23 12:56:31]

Patchset 2 (id:??) landed as
https://crrev.com/181022b6787c55ef0da34d9644eaa87b5b8d8f3c
Cr-Commit-Position: refs/heads/master@{#349137}