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This CL updates hosted app windows on Mac to paint the site's
theme colour and include the hosted app menu button and
permission icons.

This change is hidden behind the kDesktopPWAWindowing flag.

Before: https://bugs.chromium.org/p/chromium/issues/attachment?aid=363793&signed_aid=_Z4yIZ_JlJC81IRgR-cUrA==&inline=1
After: https://bugs.chromium.org/p/chromium/issues/attachment?aid=363794&signed_aid=hHrKili6tqk3XTdQPfWLiQ==&inline=1

Bug: 895690
Change-Id: I7753b5119f165dab9573cc35f6d56cafb1ccfdb8
Reviewed-on: https://chromium-review.googlesource.com/c/1290057
Commit-Queue: Alan Cutter <alancutter@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601443}