The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e3e408aed9d1b2886f984ab7e7beaddd787edfe9

commit e3e408aed9d1b2886f984ab7e7beaddd787edfe9
Author: moshayedi <moshayedi@chromium.org>
Date: Mon Apr 18 18:38:42 2016

Dispatch scroll events as mouse wheel events in mus.

This is a temporary workaround to avoid crashing on scroll events. We will
change this once we have scroll event support in mus.

BUG= 602859 

Review URL: https://codereview.chromium.org/1892883002

Cr-Commit-Position: refs/heads/master@{#387966}

[modify] https://crrev.com/e3e408aed9d1b2886f984ab7e7beaddd787edfe9/components/mus/ws/platform_display.cc

Bulk verified

The CL landed in #2 was a temporary workaround, and not a real fix.
See Issue 806338 for how Mus converting ET_SCROLL_* to ET_MOUSE_WHEEL_CHANGED can be problematic.
We need either proper Mus ET_SCROLL_* support, or conversion to/from some intermediary.

Sadrul suggested in Issue 806338  #9  that ET_SCROLL_* should be converted to gesture events.
Issue 767087 tracks adding gesture event support to Mus (event.mojom and traits).

Issue 767087 tracks similar support needed for gesture events.

I have a WIP CL that fixes this issue:
  https://chromium-review.googlesource.com/c/chromium/src/+/940607

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cbe6051098d894185a8b54e67c25ef110b3ffd3d

commit cbe6051098d894185a8b54e67c25ef110b3ffd3d
Author: Mike Wasserman <msw@chromium.org>
Date: Fri Mar 02 00:20:38 2018

mus: Support scroll event transport and dispatch

Add ScrollData and EventMomentumPhase mojo struct, enum, and traits.
Remove lossy ScrollEvent conversion code from PlatformDisplayDefault.
Generalize some EventDispatcher code to support non-pointer events.
Add a basic StructTraitsTest.ScrollEvent unit test.

Bug:  602859 , b/73663094
Test: onemilescroll.com, Arc++ scrolls/flings with --enable-features=Mus
Change-Id: Ib6ba95fdd79aa67d5ad1b6b7c4ff9f4b38b3e45b
Reviewed-on: https://chromium-review.googlesource.com/940607
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540367}
[modify] https://crrev.com/cbe6051098d894185a8b54e67c25ef110b3ffd3d/services/ui/ws/event_dispatcher.cc
[modify] https://crrev.com/cbe6051098d894185a8b54e67c25ef110b3ffd3d/services/ui/ws/event_dispatcher.h
[modify] https://crrev.com/cbe6051098d894185a8b54e67c25ef110b3ffd3d/services/ui/ws/platform_display_default.cc
[modify] https://crrev.com/cbe6051098d894185a8b54e67c25ef110b3ffd3d/ui/events/mojo/event.mojom
[modify] https://crrev.com/cbe6051098d894185a8b54e67c25ef110b3ffd3d/ui/events/mojo/event.typemap
[modify] https://crrev.com/cbe6051098d894185a8b54e67c25ef110b3ffd3d/ui/events/mojo/event_constants.mojom
[modify] https://crrev.com/cbe6051098d894185a8b54e67c25ef110b3ffd3d/ui/events/mojo/event_struct_traits.cc
[modify] https://crrev.com/cbe6051098d894185a8b54e67c25ef110b3ffd3d/ui/events/mojo/event_struct_traits.h
[modify] https://crrev.com/cbe6051098d894185a8b54e67c25ef110b3ffd3d/ui/events/mojo/struct_traits_unittest.cc