DevTools: Wait for TapGesture before acking Input.dispatchTouchEvent

A follow up patch will convert chromedriver to use dispatchTouchEvent.

Bug: chromedriver:2144
Change-Id: Ib6b04791bb46f1d09dc1fc92de257f8160d5a4f8
Reviewed-on: https://chromium-review.googlesource.com/818086
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523965}
5 files changed