Migrate iOS ClearBrowsingData tests to TestSyncService

...instead of ProfileSyncServiceMock, which is an antipattern.

Bug: 910518
Change-Id: Iec983a22725d3d766c40dbbf52953909134b7b18
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1528190
Auto-Submit: Marc Treib <treib@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641651}
3 files changed