GitLab

Window selector item indicator and drag indicators share some design
so created split_view_constants.h to share constants.

Animate the selector item indicator label, and the drag indicator
widget opacity so they fade in.

Change phantom windows to when selector item dragged over to drag
indicator.

mocks:
https://gallery.googleplex.com/projects/MCHbtQVoQ2HCZQc4sf-S_quE/files/MCEpUArMVI4QsSaRnFNKc4g8wMSJbxAVNpw

screenshots:
https://screenshot.googleplex.com/D6yHyySYLhb
https://screenshot.googleplex.com/zWwVzisZuPC
https://screenshot.googleplex.com/ZiYRYhM6i62

Test: manual, ash_unittests SplitViewWindowSelectorTest
Bug: 786119
Change-Id: Iedd5e9193e73c16f2d0b0c494a86e626b32705f6
Reviewed-on: https://chromium-review.googlesource.com/779940Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523286}