Add unrooted_must_root lint for enums and structs containing JS<T>, as well as functions with JS<T> in their parameter list

For safe wrappers over JS<T> (eg Temporary<T>) use #[allow(unrooted_must_root)].
For all other types containing a #[must_root] value, annotate the type with #[must_root] to ensure that it is never used unrooted

components/script/dom/canvasrenderingcontext2d.rs

@@ -17,6 +17,7 @@ use geom::size::Size2D;
 use canvas::canvas_render_task::{CanvasMsg, CanvasRenderTask, ClearRect, Close, FillRect, Recreate, StrokeRect};
 
 #[deriving(Encodable)]
+#[must_root]
 pub struct CanvasRenderingContext2D {
     reflector_: Reflector,
     global: GlobalField,