[Android] Add logging of active device_forwarders

[Android] Add logging of active device_forwarders

When a forwarder fails to be created, it currently attempts to kill
device_forwarder on the device. This adds logging after the kill
attempt occurs so we can confirm that the device_forwarder is killed.

BUG=520958
Committed: https://crrev.com/a32d6c654bacc903b179ade49ded6cba1a7c4443
Cr-Commit-Position: refs/heads/master@{#345607}

[rnephew (Reviews Here), 2015-08-25 21:14:58]

rnephew@chromium.org changed reviewers:
+ jbudorick@chromium.org

[jbudorick, 2015-08-26 12:58:42]

lgtm

[rnephew (Reviews Here), 2015-08-26 13:21:22]

The CQ bit was checked by rnephew@chromium.org

[commit-bot: I haz the power, 2015-08-26 13:21:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1316803002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1316803002/1

[commit-bot: I haz the power, 2015-08-26 14:37:43]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-26 14:38:25]

Patchset 1 (id:??) landed as
https://crrev.com/a32d6c654bacc903b179ade49ded6cba1a7c4443
Cr-Commit-Position: refs/heads/master@{#345607}