base

Dispatch multiple touch events in parallel.

This change enables the input dispatcher to send multiple touch
events to an application without waiting for them to be acknowledged.
Essentially this is a variation on the old streaming optimization
but it is much more comprehensive.  Event dispatch will stall as
soon as 0.5sec of unacknowledged events are accumulated or a
focused event (such as a key event) needs to be delivered.

Streaming input events makes a tremendous difference in application
performance.  The next step will be to enable batching of input
events on the client side once again.

This is part of a series of changes to improve input system pipelining.

Bug: 5963420
Change-Id: I025df90c06165d719fcca7f63eed322a5cce4a78