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- Autogenerate Polymer 3 action_link_css style module
- Add <a is="action-link"> instance in the demo page

This is in preparation of migrating chrome://extensions to Polymer3.

Bug: 965770
Change-Id: I32a51118ffd2f0cd9edad8ed3f01723002e1244f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1799466
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Auto-Submit: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695906}