Replaces gesture navigation arrow bubble drawable with a 9-patch one
that doesn't need raw color constants. And made the size a little
bigger (40dp for bubble, plus drop shadow) as suggested.

Bug: 991785, 993506
Binary-Size: Increase needed for binary resources.
Change-Id: I36da352899428291ffbbfd8797b3abec581ea9f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1771638
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691051}