Track unhandled input events in consistency verifiers.

This fixes spurious verification errors that would be generated
when a view declined an initial event such as ACTION_DOWN.  Since
the view would not receive the rest of the event stream, it would
not see the corresponding ACTION_UP and the next ACTION_DOWN would
trigger a spurious verification error.

Change-Id: I2386acf378cd1765d5446faed5ad9c6525f8b400