Bug 922147 - Pre: Remove some GlobalSession input checking.
Bug 922147 - Part 1: Add getAuthHeaderProvider.
Bug 922147 - Part 2: Remove SyncConfiguration.password.
Bug 922147 - Part 3: Replace passwords with AuthHeaderProvider.
Bug 922147 - Post: Remove SyncConfiguration.userAPI.
Bug 922147 - Review comments: Use SyncConfiguration.storageURL().
Bug 922147 - Abstract password out of Android Sync auth flow. r=rnewman