GitLab

Remove the unnecessary code from RootView::DispatchGestureEvent()
by condensing it to a single loop and moving parts of
the implementation into RootView::PreDispatchEvent() and
RootView::PostDispatchEvent().

BUG=404228
TEST=covered by existing unit tests

Review URL: https://codereview.chromium.org/517023004

Cr-Commit-Position: refs/heads/master@{#293055}