This doesn't change behavior by default but allows authors to remove the padding
previously enforced to align with focus ring padding, if they wish to.
Extra padding was created for a prospective -moz-focus-inner ring.
We now just size that ring the same as the content frame, inflated by its CSS
padding.
* Stop using a node bit for HasExplicitBaseURI
* Move MAY_HAVE_CLASS to mBoolFlags
* Add a flag to indicate that a node is native anonymous content
* Allow tagging of pseudo-implementing native anonymous content with the pseudo type at creation time, and eliminate explicit style contexts in nsIAnonymousContentCreator::ContentInfo
Tag #1375