Revert of Removing the mock-keychain related bool from GCMStore constructor

Revert of Removing the mock-keychain related bool from GCMStore constructor (https://codereview.chromium.org/221453003/)

Reason for revert:
gcm_unit_tests were disabled on a Mac because they were hanging on build bots. This is due to a combination of factors such as gcm_unit_tests not running in the CQ and possible keychain related configuration updates. In order to fix the problem step by step, this change will have to be attempted again.

Original issue's description:
> Removing the mock-keychain related bool from GCMStore constructor
> 
> Removing the first parameter of GCMStore constructor.
> Adding BuildGCMStore to GCMInternalsBuilder.
> 
> BUG=342360
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=261842

TBR=jianli@chromium.org,zea@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=342360
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=262333

[fgorski, 2014-04-08 04:48:14]

Created Revert of Removing the mock-keychain related bool from GCMStore
constructor

[commit-bot: I haz the power, 2014-04-08 04:48:18]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/fgorski@chromium.org/226223005/1

[commit-bot: I haz the power, 2014-04-08 05:32:16]

Change committed as 262333