Initial implementation of JSManaged for Events.
Make reflection work for new JSManaged types.
Generate base and derived traits and implementations for DOM types automatically.
Generate traits for casting up and down the DOM hierarchy.
Force Event and its children to use the Box representation.
Make event-related tests pass again by ensuring we're unwrapping to the correct types.
Convert Attr to JSManaged.
Convert EventTarget hierarchy to JSManaged, exlucding Window.
Convert Window to JSManaged.
Convert Blob to JSManaged.
Convert FormData to JSManaged.
Convert AttrList and HTMLCollection to JSManaged.
Convert all remaining DOM types to JSManaged, and fix some missing box representations.
Default to JSManaged for all DOM types.
Move box layout hack to Reflector.
Wrap JSManaged's inner type in RefCell.
Inhibit all GC attempts while Rust code is running to avoid JSManaged hazards.
Derive trace hooks automatically for all DOM types.
Add missing trace.rs.
Rename reflect_dom_object2 to reflect_dom_object.