[Refactor] Set input type only during ScrollBegin

This is a small cleanup that stores the passed in input source type for
the duration of a scroll latch. We can use this to replace the
|wheel_scrolling_| bit in LTHI and remove it as a param from
ScrollUpdate.

Bug: 1016229
Change-Id: I42c62e8b257ae7ffd91982676a722cf31b7da860
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1982242
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#730293}
8 files changed