Subscribed the LocationPreferenceController to listen to the location
providers changed action. This allows timely summary update. Previous
approach, directly calling the updateSummary method onResume failed in
the scenario when user changed the location settings via the
QuickSettings.
Test: Added robolectric tests, and manually verified the intended
behavior on a device.
Bug: 37956060
Change-Id: I2f81713d59da3384f3c98b327d377d529d440a88
2e52b42e3b