split view: Adjust duration of white bar animation for divider dragging

The present CL changes the duration of the animation where the divider
handle morphs into a circle when dragging starts or back to its original
shape when dragging ends. The desired duration is specified here:
https://mccanny.users.x20web.corp.google.com/www/splitscreen-motion/index.html#project-resizing

Test: manual
Bug: 953819
Change-Id: I79267c9a6d1d2451ed771068beb35593fb4724af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1572519
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#651873}