libgui: add BufferQueue test infrastructure

This change adds some infrastructure for testing the BufferQueue class.  It
also includes a test that tests the new check in BufferQueue::acquireBuffer
that prevents the consumer from acquiring more than one buffer beyond the max
acquired buffer count that was set.

Change-Id: I38554ad3f9a53d2ddeba7ef0deee35ec2e2f9775
3 files changed