Editing should not create CSSOM wrappers.

Change EditingStyle to grab the list of StyleRules directly
instead of the list of CSSRules. This means we don't do the
work of creating the CSSOMWrappers and finding their appropriate
stylesheet.

Extending the existing naming convention of having CSSRule be
the CSSOMWrapper and StyleRule be the non-wrapped rule.

Review URL: https://codereview.chromium.org/52093005

git-svn-id: svn://svn.chromium.org/blink/trunk@160977 bbb929c8-8fbe-4397-9dbb-9b2b20218538