Draft: Moving code out of ProfileSyncServiceHarness

Draft: Moving code out of ProfileSyncServiceHarness

NOT FOR COMMIT.  This is for review purposes only.

This continues the integration test refactoring.  It upgrades the
StatusChangeChecker with new features.  It uses those new features to
pull code out of the ProfileSyncServiceHarness.  I think this proves
that the ProfileSyncServiceHarness can be eliminated entirely.

Here are some of the advantages we gain from these changes:
- Configurable timeout intervals.
- Better debug messages.
- AwaitQuiescence is now stateless.
- All other multi-client Await functions replaced with AwaitQuiescence.

With a bit more work, we can move the remaining functions out of the
ProfileSyncServiceHarness.  Once that's done, we can start to replace
the generic progress-marker based Await functions with more specific
wait funcitons.

BUG=323380