Clear GCMProfileService::account_id_ when signing out

Clear GCMProfileService::account_id_ in when signing out

This fixed the bug that signing out and then signing in again does not
restart GCM.

BUG=393043
TEST=new test added

Committed: https://crrev.com/2f90d82bfba66c4b0f98ccb2ecfbb6ec2961b8c9
Cr-Commit-Position: refs/heads/master@{#293319}

[jianli, 2014-09-03 21:42:19]

jianli@chromium.org changed reviewers:
+ fgorski@chromium.org

[fgorski, 2014-09-03 22:36:58]

lgtm

[jianli, 2014-09-03 22:39:23]

The CQ bit was checked by jianli@chromium.org

[commit-bot: I haz the power, 2014-09-03 23:23:31]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jianli@chromium.org/535393002/1

[commit-bot: I haz the power, 2014-09-04 01:59:14]

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

[commit-bot: I haz the power, 2014-09-04 01:59:15]

Try jobs failed on following builders:
  android_clang_dbg_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_clang_d...)

[jianli, 2014-09-04 17:09:31]

The CQ bit was checked by jianli@chromium.org

[commit-bot: I haz the power, 2014-09-04 17:10:54]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jianli@chromium.org/535393002/1

[commit-bot: I haz the power, 2014-09-04 17:53:16]

Committed patchset #1 (id:1) as 8b1970b93f0f7ccbd05e868ded1944d7199c7c7c

[commit-bot: I haz the power, 2014-09-10 03:32:08]

Patchset 1 (id:??) landed as
https://crrev.com/2f90d82bfba66c4b0f98ccb2ecfbb6ec2961b8c9
Cr-Commit-Position: refs/heads/master@{#293319}