Bug 1289432 - Start populating the mQueuedInput array with queued input objects. r=botond

Most of the changes to InputBlockState.* are temporary and will be removed in a
future patch, once the transition to using mQueuedInputs is complete. However,
the code is useful as an intermediate step to verify that mQueuedInputs is
maintaining events in the same order and with the same lifetime as the old block-
based queue.

MozReview-Commit-ID: I8lVhMiT4hg