Change description:
A set of spec'ed convenience methods for working with DOM Nodes are not supported by Blink; we should ship these and align with both spec and other browser vendors.

Changes to API surface:
Extends the ChildNode and ParentNode DOM interfaces:
 
 * ParentNode.prepend()
 * ParentNode.append()
 * ChildNode.before()
 * ChildNode.after()
 * ChildNode.replaceWith()

Links:
https://dom.spec.whatwg.org/#childnode
https://dom.spec.whatwg.org/#parentnode

(Node implements ChildNode and ParentNode.)

Support in other browsers:
Internet Explorer: no
Firefox: yes
Safari: yes