[macOS Big Sur] New app icon

Bug: 1100642
Change-Id: I1e282150bd7c0774aa00f59012a14d1330d43f1a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2511090


Auto-Submit: Avi Drissman <avi@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Mark Mentovai <mark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822911}