Adding role 'RubyRole' in blink to expose HTML Ruby tag.

This CL will be followed by chromium side CL which will expose Ruby tag.

BUG=426893

Review URL: https://codereview.chromium.org/710663002

git-svn-id: svn://svn.chromium.org/blink/trunk@185001 bbb929c8-8fbe-4397-9dbb-9b2b20218538