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This cl is a fix for the following cl:
https://chromium-review.googlesource.com/c/chromium/src/+/1281687

The original cl fixes the crbug.com/884728 by making sure that
the GSU/GSE events with inertial phase are not bubbled to the parent.
In the original cl Mac is an exception since on this platform the GSU
events with inertial phase are received from the OS rather than being
generated by the fling controller.

What the original cl is missing is that Mac is not the only platform
on which we receive GSU events with inertial phase from OS. On Windows
devices with high precision touchpad the same thing happens.

This cl makes sure that we only stop bubbling the GSU/GSE events that are
generated from the fling controller: i.e. GSU/GSE events with inertial
phase that are either from touchscreen source or from touchpad source
but on ChromeOS only. (touchpad fling happens on chromeOS only, and on Mac
and on Windows(high precision touchpad) GSU events with inertial phase are
not generated by the fling controller.)

Bug: 884728, 897901
Change-Id: I5d620cc147707f1727c938a868a4082639095568
Reviewed-on: https://chromium-review.googlesource.com/c/1294398
Commit-Queue: Sahel Sharify <sahel@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Reviewed-by: Navid Zolghadr <nzolghadr@chromium.org>
Reviewed-by: Kevin McNee <mcnee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601765}