Bug 863103 - Add BackgroundService runIntentInService() and WakeLock

@rnewman r?

After reviewing Google's Cloud Messaging (GCM) implementation, here are two BackgroundService additions that may be useful:

1. Add runIntentInService() utility method to ensure the original Intent's extras are copied to rebroadcast Intent:

  https://code.google.com/p/gcm/source/browse/gcm-client/src/com/google/android/gcm/GCMBaseIntentService.java?r=3f8285f108caecf9ee040cdadda3a024b81f7e3e#268

2. Add WakeLock to ensure BackgroundService receives the Intent after the BroadcastReceiver returns.

GCM releases its WakeLock at the end of onHandleIntent():

  https://code.google.com/p/gcm/source/browse/gcm-client/src/com/google/android/gcm/GCMBaseIntentService.java?r=3f8285f108caecf9ee040cdadda3a024b81f7e3e#241

Can we safely assume that Android will always call our onDestroy() method? If not, then we risk leaking a WakeLock.

This change is tricky because it relies on every subclass calling super.onHandleIntent() and super.onDestroy() (if the subclass has overridden those methods). Also, we might be able to remove the ugly EXTRA_RELEASE_WAKE_LOCK extra if we assume BackgroundServices are always launched from runIntentForService() and thus called acquireWakeLock().