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 - Move some styles from shared_style_css.html to paper_button_style_css.html.
 - Update paper-button styles per latest spec.
 - Collapse previously different types of buttons "primary" and "action" into a
   single button type.

Note this change is intentionally changing the shared styling for buttons. If a
certain WebUI page needs a different pre-MD refresh style, should be updated
individually to override (hopefully there are no such cases though).

Bug: 832173
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I8558db8ffd121ad09b100f8ba6ab4d843022f73f
Reviewed-on: https://chromium-review.googlesource.com/1013330
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Scott Chen <scottchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553382}