Add extra key to StreamingCall.

Also fix bug where CallStreamingService would never init the streaming
adapter.  This caused the CallStreamingService to NEVER get notified of
onCallStreamingstarted since the handleMessage method was checking to see
if the adapter was set.

Test: Added CTS test for this case.
Bug: 279650527
Change-Id: I389efacd7547439985caabc068be5413897cf128