Make slight API and doc adjustments

* Fix a compile error on Java 7
* Update initialization mechanism to allow exceptions and return codes
* App-facing api for StreamingService#dispose no longer throws an
IllegalArgumentException
* Add REASON_NONE to stream state change reasons

Bug: 30981736
Change-Id: I4710c6e56b35f74188f5877f0cf74b7773c1e9b7