Android Chromoting: Add hooks for the official account-switcher

Android Chromoting: Add hooks for the official account-switcher

This adds some GYP variables to allow official builds to modify the
remoting_apk target.
Also adds a destroy() method to the interface, to release resources
used by the account-switcher.
Also adds hooks to allow the account-switcher to gracefully
handle connection errors to Google Play Services.

BUG=517688
Committed: https://crrev.com/f3ffeee66a9abc6bf99860430d81c8396cc8e763
Cr-Commit-Position: refs/heads/master@{#351693}

[Lambros, 2015-09-26 05:19:49]

lambroslambrou@chromium.org changed reviewers:
+ sergeyu@chromium.org

[Sergey Ulanov, 2015-09-28 19:14:51]

lgtm

[Lambros, 2015-09-29 18:28:17]

PTAL, added more hooks.

[Sergey Ulanov, 2015-10-01 00:28:24]

lgtm

[Lambros, 2015-10-01 00:31:43]

The CQ bit was checked by lambroslambrou@chromium.org

[commit-bot: I haz the power, 2015-10-01 00:32:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1369903002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1369903002/20001

[commit-bot: I haz the power, 2015-10-01 01:09:49]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-01 01:10:35]

Patchset 2 (id:??) landed as
https://crrev.com/f3ffeee66a9abc6bf99860430d81c8396cc8e763
Cr-Commit-Position: refs/heads/master@{#351693}