fix [2835280] Add support for cancelling buffers to ANativeWindow

There is a new ANativeWindow::cancelBuffer() API that can be used to
cancel any dequeued buffer, BEFORE it's been enqueued. The buffer is
returned to the list of availlable buffers. dequeue and cancel are not
mutually thread safe, they must be called from the same thread or
external synchronization must be used.

Change-Id: I86cc7985bace8b6a93ad2c75d2bef5c3c2cb4d61