Previously the IDL definition for toggleAttribute doesn't have
those modifiers, so they behave differently than setAttribute when
called on custom elements (it won't fire attributeChangedCallback, etc)
Bug: 976177

Change-Id: I7d8107db8d07a2e2ec856305c56a178339c5e05c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663881


Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Auto-Submit: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670060}