[TSan flakiness] Init feature lists in the fixture in wallet sync tests

This CL fixes TSan flakiness for wallet sync_integration_tests. TSan
reports a data race if ScopedFeatureList gets initialized in the body
of the test.

Bug: 915219
Change-Id: Ia3ea05c9aabf49de40281238991cf2c2caa2fb57
Reviewed-on: https://chromium-review.googlesource.com/c/1411914
Commit-Queue: Jan Krcal <jkrcal@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622855}
3 files changed