Remove largely unused event processing from layout system

Most layouts use an event filter to handle input. There exists a
second input handling system in layout that is now only used by the
toolbar swipe layout. This patch removes the unused plumbing and
isolates the code that toolbar swipe uses. Conversion to the newer
event filter system will happen in a later patch.

Bug: 882508
Change-Id: Ib8d80c34e75a8e587f8db65bbf996541970b7057
Reviewed-on: https://chromium-review.googlesource.com/1225881
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#591365}
6 files changed