Add owners for MessageQueue related files

We've been profiling and making improvements to MessageQueue for
some time now and also have OWNERS for MessageQueueTest.java. Would
like to be able to review future changes to the core MessageQueue
class. I also added Message.java for good measure.

Test: presubmit
Change-Id: I961a2468c7b9a451d3b33d78a67f17cccf22cd60