SearchTabHelper: Add IsSyncFeatureEnabled check to IsHistorySyncEnabled

Previously it just checked GetPreferredDataTypes. This was probably
okay in practice (the check was anyway more of a "has the user not
disabled history sync" rather than "is history sync enabled"), but
still better to be correct.

While we're here, also move to SyncUserSettings, which is the new way
to query any user-configurable bits of Sync.

This also includes a bunch of test cleanup: Removing a Mock class that
isn't used, and using NiceMock to avoid unnecessary chattiness.

Bug: 907027, 884159
Change-Id: I2a3d0f8ef13a74b51f4b4a2edc19976a61c6c430
Reviewed-on: https://chromium-review.googlesource.com/c/1343087
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610055}
2 files changed