Replace aria-active-attribute in WebUI

With the switch to cr-button from paper-button, the component no longer
has support for aria-active-attribute. Instead we simply set the
expanded value via an element attribute binding.

Bug: 967793
Change-Id: I033c025aa25160ede9271cd5e8725e61630183f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1798342
Reviewed-by: Esmael Elmoslimany <aee@chromium.org>
Commit-Queue: Martin Robinson <mrobinson@igalia.com>
Cr-Commit-Position: refs/heads/master@{#695723}
4 files changed