[Sync] Convert SyncSessions to NonUIDataTypeController and remove UIDataTypeController

[Sync] Convert SyncSessions to NonUIDataTypeController and remove UIDataTypeController

In this change I:
- Switched SessionDataTypeController to NonUIDataTypeController
- Refactored SessionsSyncManager to only dereference local_device_ in
  MergeDataAndStartSyncing. This ensures that clearing local_device_ either
  doesn't affect SessionsSyncManager or gets properly reproted.
- Since local event notifications can come between PSS::ShutdownImpl and
  StopSyncing, MergeDataAndStartSyncing can fail because local_device_ was
  cleared. I changed RebuildAssociations to recognize this and not to fail
  DCHECK in OnLocalTabModified.

BUG=647505
R=maxbogue@chromium.org

Committed: https://crrev.com/d8529e23dd0a239bf2132178e0c7dc53b9010e58
Cr-Commit-Position: refs/heads/master@{#436394}

[pavely, 2016-12-02 20:15:06]

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

[commit-bot: I haz the power, 2016-12-02 20:15:39]

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, 2016-12-02 20:41:38]

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

[commit-bot: I haz the power, 2016-12-02 20:41:39]

Dry run: Try jobs failed on following builders:
  ios-simulator on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-simulator/bui...)

[pavely, 2016-12-02 21:22:05]

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

[commit-bot: I haz the power, 2016-12-02 21:22:51]

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, 2016-12-02 23:05:28]

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

[commit-bot: I haz the power, 2016-12-02 23:05:29]

Dry run: This issue passed the CQ dry run.

[maxbogue, 2016-12-05 18:47:20]

lgtm

[pavely, 2016-12-05 19:13:57]

The CQ bit was checked by pavely@chromium.org

[commit-bot: I haz the power, 2016-12-05 19:14:28]

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, 2016-12-05 20:43:24]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1480965237901770,
"parent_rev": "1c3c0932c53a559b80c8f661b80c8b2f64ae970a", "commit_rev":
"104fe9d97d55ebeea29bc45bdbc5e932d9bedfb0"}

[commit-bot: I haz the power, 2016-12-05 20:43:51]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-12-05 20:47:20]

Description was changed from

==========
[Sync] Convert SyncSessions to NonUIDataTypeController and remove
UIDataTypeController

In this change I:
- Switched SessionDataTypeController to NonUIDataTypeController
- Refactored SessionsSyncManager to only dereference local_device_ in
  MergeDataAndStartSyncing. This ensures that clearing local_device_ either
  doesn't affect SessionsSyncManager or gets properly reproted.
- Since local event notifications can come between PSS::ShutdownImpl and
  StopSyncing, MergeDataAndStartSyncing can fail because local_device_ was
  cleared. I changed RebuildAssociations to recognize this and not to fail
  DCHECK in OnLocalTabModified.

BUG=647505
R=maxbogue@chromium.org
==========

to

==========
[Sync] Convert SyncSessions to NonUIDataTypeController and remove
UIDataTypeController

In this change I:
- Switched SessionDataTypeController to NonUIDataTypeController
- Refactored SessionsSyncManager to only dereference local_device_ in
  MergeDataAndStartSyncing. This ensures that clearing local_device_ either
  doesn't affect SessionsSyncManager or gets properly reproted.
- Since local event notifications can come between PSS::ShutdownImpl and
  StopSyncing, MergeDataAndStartSyncing can fail because local_device_ was
  cleared. I changed RebuildAssociations to recognize this and not to fail
  DCHECK in OnLocalTabModified.

BUG=647505
R=maxbogue@chromium.org

Committed: https://crrev.com/d8529e23dd0a239bf2132178e0c7dc53b9010e58
Cr-Commit-Position: refs/heads/master@{#436394}
==========

[commit-bot: I haz the power, 2016-12-05 20:47:21]

Patchset 2 (id:??) landed as
https://crrev.com/d8529e23dd0a239bf2132178e0c7dc53b9010e58
Cr-Commit-Position: refs/heads/master@{#436394}