Fix a crash on clearing power consumption auditing data in guest mode.

Fix a crash on clearing power consumption auditing data in guest mode.

Add a null check on OriginPowerMap, since it is possible to get NULL from
OriginPowerMapFactory::GetForBrowserContext() in guest mode.

BUG=416374
Committed: https://crrev.com/295b5348163f19a8993b2f16b74bdb3936bbfea7
Cr-Commit-Position: refs/heads/master@{#296280}

[babu, 2014-09-23 12:46:56]

sudarsana.nagineni@intel.com changed reviewers:
+ dhnishi@chromium.org, markusheintz@chromium.org

[markusheintz_, 2014-09-23 17:54:58]

LGTM

[babu, 2014-09-23 21:03:26]

The CQ bit was checked by sudarsana.nagineni@intel.com

[commit-bot: I haz the power, 2014-09-23 21:06:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/598543002/1

[commit-bot: I haz the power, 2014-09-23 22:13:28]

Committed patchset #1 (id:1) as 3faaeed8cfd43a9a4130b3f8b4ee1d623848ffaa

[commit-bot: I haz the power, 2014-09-23 22:14:35]

Patchset 1 (id:??) landed as
https://crrev.com/295b5348163f19a8993b2f16b74bdb3936bbfea7
Cr-Commit-Position: refs/heads/master@{#296280}