DevTools: Wait for ack when dispatching mousePressed and mouseReleased

The protocol command Input.dispatchMouseEvent will now wait for
mousedown and mouseup events to be dispatched into the page JavaScript.

Bug: 747647
Change-Id: Icea417e1ead2fbc7d14f950cc8d731baab88261d
Reviewed-on: https://chromium-review.googlesource.com/609523
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#493596}
3 files changed