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- Autogenerate Polymer 3 cr-tooltip-icon. This is used by the
chrome://extensions page directly (rather than through a pref
indicator).
- Add to the demo page
- Small update to demo page styling so that elements are spaced out a
bit.

Bug: 965770
Change-Id: Id22953537a3968ce471f1c40221a8ffc68fa9b0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787169
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Esmael Elmoslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694993}