Revert "Synthetic gestures wait on renderer ACK."

This reverts commit 91d6c20eccf8a67a4dd29f0102f526193db6b06a.

Reason for revert: external/wpt/pointerevents/pointerevent_lostpointercapture_for_disconnected_node.html is flaky (see https://crbug.com/920581)

Original change's description:
> Synthetic gestures wait on renderer ACK.
> 
> Currently, synthetic gestures invoke the "completed callback" as soon as
> the final gesture has been dispatched. This causes issues in client
> code, typically tests, that want to wait until the effects of a gesture
> are complete before sending further input or checking page state.
> 
> This CL is the first step in a series of CLs to make this completion
> callback reliable. We add a new API in the renderer that resolves the
> completion callback once the input has been fully processed by the
> renderer. For now, this method just ACKs immediately but its
> implementation will be further fleshed out in a followup CL.
> 
> Bug: 902446
> Change-Id: I96f2f4b8fce5234ede83c3ec49abce840d1b6eda
> Reviewed-on: https://chromium-review.googlesource.com/c/1390327
> Reviewed-by: Avi Drissman <avi@chromium.org>
> Reviewed-by: Robert Sesek <rsesek@chromium.org>
> Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
> Commit-Queue: David Bokan <bokan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#621320}

TBR=avi@chromium.org,bokan@chromium.org,dtapuska@chromium.org,rsesek@chromium.org

Change-Id: I0fda381b12cdbff8c27f6602967bb8a233272676
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 902446
Reviewed-on: https://chromium-review.googlesource.com/c/1405008
Reviewed-by: Roman Sorokin <rsorokin@chromium.org>
Commit-Queue: Roman Sorokin <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621570}
38 files changed