There was a race condition in ProfileSyncServiceHarness due to its multiple
inheritance of ProfileSyncServiceObserver and NotificationObserver,
causing several integration tests to fail.

This patch contains a fix that involves not inheriting from
NotificationObserver, and simply relying on the OnStateChanged()
mechanism of ProfileSyncServiceObserver, thereby eliminating the race.

It also contains 2 new test cases that further verify passphrase functionality:
SetPassphraseAndThenSetupSync and SetPassphraseTwice.

BUG=64109
TEST=sync_integration_tests

Review URL: http://codereview.chromium.org/5801003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@69203 0039d316-1c4b-4281-b951-d872f2087c98