* Replaced all occurrances of paper-button with cr-button.
* Removed paper_button_style.css.
* Added cr-button template style overrides to polymer_overriding.
* Patched polymer.html to include polymer_overriding and removed
polymer_overriding from brave_settings_overrides.

Chromium change:

Removal of paper-button:
https://chromium.googlesource.com/chromium/src/+/03d1652fb3cecd58f02ce783da958901cc2c31db

commit 03d1652fb3cecd58f02ce783da958901cc2c31db
Author: Esmael El-Moslimany <aee@chromium.org>
Date:   Wed Jul 10 21:58:43 2019 +0000

    WebUI: remove paper-button from third_party/polymer

    Bug: 967793

Bug link with other commits:
https://bugs.chromium.org/p/chromium/issues/detail?id=967793