Reland CrOS Shelf: Change hotseat color between in-app and home shelf.

This is a reland which has fixed msan failures by initializing
|target_color_| in hotseat_widget.cc.

In this change, the hotseat background will change color for different
shelf states and will animate between colors when changing. When in-app
shelf is shown the hotseat color should have an alpha value of 90%.
When the home shelf is shown the hotseat color should have an alpha
value of 60%.

Bug: 1041132
Change-Id: I74c1fc9de07d7db1e39400a963d6a5c7c8149320
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2017913
Reviewed-by: Manu Cornet <manucornet@chromium.org>
Commit-Queue: Matthew Mourgos <mmourgos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735098}
2 files changed