GitLab

* Add MdIPHBubbleButton, a transparent MD button with optional
white border.
* Add snoozable option to IPH bubble. Disable auto-dismiss for
snoozable button.

UX spec: https://docs.google.com/presentation/d/1l19RBFdJjsLIO2KPVANY-ObfwmUCkpQ1Lj8IeLAqJZM/edit#slide=id.g92aa3ae4f7_1_43
Screenshot: https://screenshot.googleplex.com/5brgyBvGcaoMeEP


Bug: 1121399
Change-Id: Ic3ca76b6edcb52bdc9d856aa6ee11476e018218d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2394157Reviewed-by: Wei Li <weili@chromium.org>
Reviewed-by: Collin Baker <collinbaker@chromium.org>
Commit-Queue: Keren Zhu <kerenzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805592}