Reuse one UserPolicySigninService for Android and iOS.

Reuse one UserPolicySigninService for Android and iOS.

This change unifies the UserPolicySigninServices for Android and iOS
into one class, to remove code duplication.

The iOS version also gets support for recovering from offline signins:
the policy registration will be performed on the next restart in that
case, and checked again every 24 hours.

BUG=273055, 344403, 278027
TBR=nyquist@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=268178

[Joao da Silva, 2014-05-05 10:12:42]

Daniel, PTAL. This is an upstreaming of
https://chromereviews.googleplex.com/40847013.

Bin, FYI. Feel free to start working on http://crbug.com/278027 after this
lands.

[Joao da Silva, 2014-05-05 11:32:35]

This change is the same as from downstream, but it needed some fixes to build on
Android (see delta from patch set 2 to 1).

[dconnelly, 2014-05-05 11:40:19]

lgtm

[Joao da Silva, 2014-05-05 12:57:53]

The CQ bit was checked by joaodasilva@chromium.org

[commit-bot: I haz the power, 2014-05-05 12:57:59]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/joaodasilva@chromium.org/264043008/20001

[commit-bot: I haz the power, 2014-05-05 14:38:38]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  chromium_presubmit on tryserver.chromium

[Joao da Silva, 2014-05-05 14:40:55]

+Tommy to TBR for the header update to signin_manager_android.cc

[commit-bot: I haz the power, 2014-05-05 14:47:07]

Change committed as 268178

[nyquist, 2014-05-06 05:39:34]

lgtm