The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c

commit c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c
Author: skym <skym@chromium.org>
Date: Tue Jun 06 18:38:53 2017

[Sync] Support commit only types.

The main differences of commit only types is that they do not have a
progress marker, they use very few metadata fields of SyncEntity, they
do not perform GetUpdates, and they delete themselves after commit
confirmation. Also only supposed on USS/NonBlocking path.

This CL updates internal sync logic to facilitate commit only types.
With these changes user events should be entirely functional on the
client. Can specify the flag --enable-features=SyncUserEvents and
existing translate integration will start emitting.

The difference between using the static CommitOnlyTypes.Has(...), vs a
private boolean in worker vs processor is unfortunate. I think the
CommitOnlyTypes.Has(...) approach is better whenever something has the
model type, however, current unit tests are tightly coupled with
PREFERENCES, which is why I created the |commit_only_| field.

BUG= 719041 

Review-Url: https://codereview.chromium.org/2916133002
Cr-Commit-Position: refs/heads/master@{#477350}

[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/base/model_type.h
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/driver/data_type_manager_impl.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/engine_impl/cycle/nudge_tracker.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/engine_impl/model_type_worker.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/engine_impl/model_type_worker_unittest.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/engine_impl/non_blocking_type_commit_contribution.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/engine_impl/non_blocking_type_commit_contribution.h
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/engine_impl/syncer.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/engine_impl/syncer_unittest.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/model/model_type_change_processor.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/model_impl/shared_model_type_processor.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/model_impl/shared_model_type_processor.h
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/model_impl/shared_model_type_processor_unittest.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/syncable/model_type.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/test/engine/mock_connection_manager.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/user_events/user_event_sync_bridge.cc
[modify] https://crrev.com/c15b61bdf8133f14d7f715ee6e0dcc5ab65db57c/components/sync/user_events/user_event_sync_bridge_unittest.cc