PyAuto hooks for Sync in TestingAutomationProvider

This patch exposes hooks for sync in TestingAutomationProvider that the chrome pyauto test suite can use. It contains the following changes:

- Partial revert of an earlier change to ProfileSyncServiceHarness. Some of its methods were made pure virtual, but this ended up being unnecessary. Also ripped out unnecessary code from LiveSyncTest.
- Minor refactor of ProfileSyncServiceHarness to allow for scenarios where the browser is restarted.
- A bunch of new methods in TestingAutomationProvider: SignInToSync, GetSyncInfo, AwaitSyncCycleCompletion, EnableSyncForDatatypes and DisableSyncForDatatypes.
- A new method in model_type.h/cc called ModelTypeFromString. Required for automation.
- New APIs in pyauto.py for sync.
- New test suite sync.py with sample tests.

BUG=53651, 60970, 56460, 61639
TEST=run pyauto sync tests

Review URL: http://codereview.chromium.org/4096004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@64988 0039d316-1c4b-4281-b951-d872f2087c98