Only process passback transactions during onFrameAvailable

A callback will be fired from the rendering thread when drawFrame
returns after queueBuffer.  Since the client expects the transaction, if
sent, to be populated with the desired frame at this time, we need to
make that call to queueBuffer wait until the frame has actually been
processed and not put on the shadow queue

Step 1 in resolving screen freeze
Bug: 149315421
Test: build, boot, turn BLAST ON & reboot & phone boots fine

Change-Id: Ibef45fe6c7e0b57fdc4a1be61e2ac93fb2d33525