Clean up input event struct traits.

Seems tap_count was not populated and there was some unreachable code.
Reorder the code so it matches the definition in the struct.

BUG=722928

Change-Id: I30f208d0b1222768aea31ba7e2cb92b488ff34fc
Reviewed-on: https://chromium-review.googlesource.com/779663


Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518264}