Track USB alternate interface state in Blink.

Track USB alternate interface state in Blink.

This patch adds logic to track which alternate interface has been
selected. This isn't too interesting by itself but is a step towards
knowing which endpoints are available.

BUG=593164
Committed: https://crrev.com/92c1f849580dea46a5ddc1a3762a86ea5a9b7cf4
Cr-Commit-Position: refs/heads/master@{#382486}

[Reilly Grant (use Gerrit), 2016-03-21 20:52:38]

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

[Reilly Grant (use Gerrit), 2016-03-21 20:52:38]

Please take a look.

[juncai, 2016-03-22 01:01:00]

LGTM with nits.

https://codereview.chromium.org/1806163002/diff/20001/third_party/WebKit/Layo...
File third_party/WebKit/LayoutTests/usb/usbDevice.html (right):

https://codereview.chromium.org/1806163002/diff/20001/third_party/WebKit/Layo...
third_party/WebKit/LayoutTests/usb/usbDevice.html:314: }, 'cannot select a
non-existant alternate interface');
nit: typo
existant -> existent

[Reilly Grant (use Gerrit), 2016-03-22 01:40:08]

The CQ bit was checked by reillyg@chromium.org

[Reilly Grant (use Gerrit), 2016-03-22 01:40:08]

The patchset sent to the CQ was uploaded after l-g-t-m from juncai@chromium.org
Link to the patchset: https://codereview.chromium.org/1806163002/#ps40001
(title: "Fixed typo and rebased.")

[commit-bot: I haz the power, 2016-03-22 01:40:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1806163002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1806163002/40001

[commit-bot: I haz the power, 2016-03-22 02:59:17]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2016-03-22 03:00:30]

Description was changed from

==========
Track USB alternate interface state in Blink.

This patch adds logic to track which alternate interface has been
selected. This isn't too interesting by itself but is a step towards
knowing which endpoints are available.

BUG=593164
==========

to

==========
Track USB alternate interface state in Blink.

This patch adds logic to track which alternate interface has been
selected. This isn't too interesting by itself but is a step towards
knowing which endpoints are available.

BUG=593164

Committed: https://crrev.com/92c1f849580dea46a5ddc1a3762a86ea5a9b7cf4
Cr-Commit-Position: refs/heads/master@{#382486}
==========

[commit-bot: I haz the power, 2016-03-22 03:00:31]

Patchset 3 (id:??) landed as
https://crrev.com/92c1f849580dea46a5ddc1a3762a86ea5a9b7cf4
Cr-Commit-Position: refs/heads/master@{#382486}