[Sync] Remove SyncClient dep from SyncBackendRegistrar.

[Sync] Remove SyncClient dep from SyncBackendRegistrar.

Instead, just pass in a factory function to create ModelSafeWorkers.

This change also includes various cleanups of the test file:

- No more need for FakeSyncClient.
- Don't take SBR as a param to functions that don't need it.
- Actually have a private section so it's clear what the tests use.
- Move a couple functions to better places.

BUG=663125
Committed: https://crrev.com/e238f9653ed383542f2121f38428928c6c619e38
Cr-Commit-Position: refs/heads/master@{#432399}

[maxbogue, 2016-11-15 21:05:02]

The CQ bit was checked by maxbogue@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-11-15 21:05:31]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-11-15 21:22:41]

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

[commit-bot: I haz the power, 2016-11-15 21:22:42]

Dry run: Try jobs failed on following builders:
  cast_shell_linux on master.tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/cast_shell_linu...)

[maxbogue, 2016-11-15 22:09:43]

The CQ bit was checked by maxbogue@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-11-15 22:10:10]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[maxbogue, 2016-11-15 22:24:15]

maxbogue@chromium.org changed reviewers:
+ pavely@chromium.org

[maxbogue, 2016-11-15 22:24:16]

Pavel, PTAL!

[commit-bot: I haz the power, 2016-11-15 22:39:13]

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

[commit-bot: I haz the power, 2016-11-15 22:39:14]

Dry run: Try jobs failed on following builders:
  mac_chromium_rel_ng on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[pavely, 2016-11-16 02:04:04]

lgtm

[maxbogue, 2016-11-16 02:14:33]

The CQ bit was checked by maxbogue@chromium.org

[commit-bot: I haz the power, 2016-11-16 02:15:10]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-11-16 06:36:52]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-11-16 06:39:36]

Description was changed from

==========
[Sync] Remove SyncClient dep from SyncBackendRegistrar.

Instead, just pass in a factory function to create ModelSafeWorkers.

This change also includes various cleanups of the test file:

- No more need for FakeSyncClient.
- Don't take SBR as a param to functions that don't need it.
- Actually have a private section so it's clear what the tests use.
- Move a couple functions to better places.

BUG=663125
==========

to

==========
[Sync] Remove SyncClient dep from SyncBackendRegistrar.

Instead, just pass in a factory function to create ModelSafeWorkers.

This change also includes various cleanups of the test file:

- No more need for FakeSyncClient.
- Don't take SBR as a param to functions that don't need it.
- Actually have a private section so it's clear what the tests use.
- Move a couple functions to better places.

BUG=663125

Committed: https://crrev.com/e238f9653ed383542f2121f38428928c6c619e38
Cr-Commit-Position: refs/heads/master@{#432399}
==========

[commit-bot: I haz the power, 2016-11-16 06:39:37]

Patchset 2 (id:??) landed as
https://crrev.com/e238f9653ed383542f2121f38428928c6c619e38
Cr-Commit-Position: refs/heads/master@{#432399}