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Previously the Dismiss button on notification opt in view is not
focus traversable when navigating through the tab key. This CL fixes
this issue by replacing it with the existing |InterstitialViewButton|
which is focusable by default and shares the common setup of system menu
buttons.

Screenshot: https://screenshot.googleplex.com/4qjFN3Aqm9rKENp.png

BUG=1106937,1126208

Change-Id: I12da67a65f064793322628c5bb5a5ea1f45dee43
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2466977Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Tim Song <tengs@chromium.org>
Commit-Queue: Meilin Wang <meilinw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816783}