ConsumerBase: free buffers outside the lock

This change makes ConsumerBase::onBuffersReleased hold a reference to all its
gralloc buffers until after the mutex is unlocked.  This prevents slow
gralloc::free calls from causing lock contention with rendering threads.

Bug: 7675940
Change-Id: I0ec805d1b612afeeecfffec03f982371d27d93be
1 file changed