Make minor edits for style to Shadow DOM 101.
Merge pull request #296 from mikewest/xss

Check the origin of messages sent to evalbox's frame.
Merge branch 'shadowdom' of https://github.com/coonsta/www.html5rocks.com into coonsta-shadowdom

Conflicts:
	content/tutorials/webcomponents/shadowdom-adv/en/index.html
Tweaked the Add New Resource page to remind of common mistakes.
First pass at a MessageChannel demo.