The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/47c2232d3a2cbad52c1f38696f37ece1f0c8154c

commit 47c2232d3a2cbad52c1f38696f37ece1f0c8154c
Author: pnoland <pnoland@chromium.org>
Date: Fri Apr 28 23:06:40 2017

[sync] Purge directory data when migrating to USS

Make use of the existing PurgeEntriesWithTypeIn to purge the directory
of entries of the type we just migrated. Add a test that ensures this
happens.

R=skym@chromium.org

BUG= 716156 

Review-Url: https://codereview.chromium.org/2842373004
Cr-Commit-Position: refs/heads/master@{#468170}

[modify] https://crrev.com/47c2232d3a2cbad52c1f38696f37ece1f0c8154c/components/sync/engine_impl/model_type_registry.cc
[modify] https://crrev.com/47c2232d3a2cbad52c1f38696f37ece1f0c8154c/components/sync/engine_impl/model_type_registry_unittest.cc