Add a queue of pending finished input events.

Although in practice an application or IME is unlikely to fill up
the input channel with finish events, it can happen when events are
being delivered very rapidly.  Handle this situation by queuing
up the pending finish events until the socket becomes writable again.

Bug: 9034301
Change-Id: I938a62a75d12106a19cff2d016ba7af0db877ecf