Rename Root<T> to DomRoot<T>

In a later PR, DomRoot<T> will become a type alias of Root<Dom<T>>,
where Root<T> will be able to handle all the things that need to be
rooted that have a stable traceable address that doesn't move for the
whole lifetime of the root. Stay tuned.

components/script/dom/canvaspattern.rs

@@ -5,7 +5,7 @@
 use canvas_traits::canvas::{FillOrStrokeStyle, RepetitionStyle, SurfaceStyle};
 use dom::bindings::codegen::Bindings::CanvasPatternBinding;
 use dom::bindings::reflector::{Reflector, reflect_dom_object};
-use dom::bindings::root::Root;
+use dom::bindings::root::DomRoot;
 use dom::canvasgradient::ToFillOrStrokeStyle;
 use dom::globalscope::GlobalScope;
 use dom_struct::dom_struct;
@@ -49,7 +49,7 @@ impl CanvasPattern {
                surface_size: Size2D<i32>,
                repeat: RepetitionStyle,
                origin_clean: bool)
-               -> Root<CanvasPattern> {
+               -> DomRoot<CanvasPattern> {
         reflect_dom_object(box CanvasPattern::new_inherited(surface_data, surface_size,
                                                             repeat, origin_clean),
                            global,