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This CL replaces the gray outline of the navigation bubble with a
shadow. Also fixes a bug on Kitkat where the bubble appears in dark
gray which was a side effect from RippleBackgroundHelper.

Bug: 979499, 988341
Change-Id: Ibea69d60834d916f99ec7add54e1d4ae7484c5e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1722581Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683489}