This class also uses PO2TS to revoke credentials; this should be converted to AccountsMutator.

Finally, the unittest should be converted to use IdentityTestEnvironment.

CL (1/2): https://chromium-review.googlesource.com/c/chromium/src/+/1387393

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a59054d082649116a5656724026a872c3ac1c4c6

commit a59054d082649116a5656724026a872c3ac1c4c6
Author: Antonio Gomes <tonikitoo@igalia.com>
Date: Fri Dec 21 20:59:14 2018

[s13n] Convert c/b/ui/webui/signin/dice_turn_sync_on_helper.cc to IdentityManager

SigninManager, PO2TS and AccountTrackerService are going to be an implementation
detail of the IdentityManager et al, and eventually will not be exposed to clients
out of //services/identity.
This CL converts DiceTurnSyncOnHelper and its subclasses accordingly.

The remaing work is the completely removal of the use of PO2TS in production
code, which is blocked on  bug 907901  (PO2TS::RevokeCredentials).

BUG=890811, 890812 

Change-Id: I5673c254e2ce494293627616f596945945d6ded1
Reviewed-on: https://chromium-review.googlesource.com/c/1387393
Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#618594}
[modify] https://crrev.com/a59054d082649116a5656724026a872c3ac1c4c6/chrome/browser/ui/webui/signin/dice_turn_sync_on_helper.cc
[modify] https://crrev.com/a59054d082649116a5656724026a872c3ac1c4c6/chrome/browser/ui/webui/signin/dice_turn_sync_on_helper.h
[modify] https://crrev.com/a59054d082649116a5656724026a872c3ac1c4c6/chrome/browser/ui/webui/signin/dice_turn_sync_on_helper_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/652ff7525dc61a51620a118d2ddd0d0c3aa9bae3

commit 652ff7525dc61a51620a118d2ddd0d0c3aa9bae3
Author: Antonio Gomes <tonikitoo@igalia.com>
Date: Thu Jan 03 21:54:26 2019

Clean up pass on DiceTurnSyncOnHelper code

This is a follow up CL to [1], that addresses post-land feedback from blundell@.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1387393/6#message-5b6d62524d8612f8d9b11bd7500af41f4f10cc76

BUG=890811, 890812 

Change-Id: Ie01be10511872dca5b053d20386559d2975e4bff
Reviewed-on: https://chromium-review.googlesource.com/c/1391688
Reviewed-by: Colin Blundell <blundell@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#619771}
[modify] https://crrev.com/652ff7525dc61a51620a118d2ddd0d0c3aa9bae3/chrome/browser/ui/webui/signin/dice_turn_sync_on_helper.cc
[modify] https://crrev.com/652ff7525dc61a51620a118d2ddd0d0c3aa9bae3/chrome/browser/ui/webui/signin/dice_turn_sync_on_helper.h
[modify] https://crrev.com/652ff7525dc61a51620a118d2ddd0d0c3aa9bae3/chrome/browser/ui/webui/signin/dice_turn_sync_on_helper_unittest.cc

Added a bug for the creation of the equivalent of ExtractCredentials().