Add support for local font faces. Improves fonts on rust lang and guide.
Create an almost-correct form_owner() for convenience
Add form submission via input element
Add click handler for <input type=submit>
Filter out buttons which aren't the submitter while constructing the dataset
Update wpt expectations
Address review comments
auto merge of #3652 : Manishearth/servo/form-button, r=jdm

Partially fixes #3647
script: Use atom comparison in more places, especially for attributes.

75% improvement in style recalc for Guardians of the Galaxy.
auto merge of #3675 : glennw/servo/local-fonts, r=pcwalton
auto merge of #3623 : pcwalton/servo/use-atoms-2, r=jdm

75% improvement in style recalc for Guardians of the Galaxy.
Add DOMRefCell<T> for safe borrowing in layout.
Use DOMRefCell<T> in element.rs.
fixup! Use DOMRefCell<T> in element.rs.
Revert "fixup! Use DOMRefCell<T> in element.rs."

This reverts commit 145338fd94abc39ae6eb695dc5c5ef1712db516e.
Revert "Use DOMRefCell<T> in element.rs."

This reverts commit d1ae985322e6de6d0212012af142ad19eb6415da.
Revert "Add DOMRefCell<T> for safe borrowing in layout."

This reverts commit b095ab3fbc354846a1a7148890c4ab1933708017.
Add DOMRefCell<T> for safe borrowing in layout.

This type simply wraps `RefCell<T>` to add the special method,
and introduce the method to return the pointer of the value contained in
itself, for used in layout task.
Use DOMRefCell<T> in Attr.
Use DOMRefCell<T> in Element.