Create profile_sync_test_util in components

There are already such utils in //chrome/browser/sync and the //ios version as
well. This CL starts by pulling out some trivial parts into a common file in
//components. More will follow as ProfileSyncService unittests will get
componentised.

BUG=544972

Review URL: https://codereview.chromium.org/1607473003

Cr-Commit-Position: refs/heads/master@{#370659}
9 files changed