Wire up component cloud policy to device local accounts.

Wire up component cloud policy to device local accounts.

Note: this is a reland of https://codereview.chromium.org/341043005 which was
reverted due to memory leaks in tests. Those leaks were fixed in
https://codereview.chromium.org/348713004.

This enables policy-for-extensions running in Public Sessions, and for
extensions running as Kiosk Apps too.

TBR=bartfab@chromium.org
BUG=224596
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=278734

[Joao da Silva, 2014-06-20 11:11:56]

The CQ bit was checked by joaodasilva@chromium.org

[commit-bot: I haz the power, 2014-06-20 11:13:23]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/joaodasilva@chromium.org/335113008/1

[commit-bot: I haz the power, 2014-06-20 14:50:09]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_gpu_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu_triggered...)

[commit-bot: I haz the power, 2014-06-20 15:23:15]

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

[commit-bot: I haz the power, 2014-06-20 15:23:16]

Try jobs failed on following builders:
  win_gpu_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu_triggered...)

[Joao da Silva, 2014-06-20 17:12:28]

Committed patchset #2 manually as r278734 (presubmit successful).