implement PartialEq for MutHeap<JS<T>> and MutNullableHeap<JS<T>>

components/script/dom/bindings/js.rs

@@ -260,6 +260,12 @@ impl<T: HeapGCValue> HeapSizeOf for MutHeap<T> {
     }
 }
 
+impl<T: Reflectable> PartialEq for MutHeap<JS<T>> {
+   fn eq(&self, other: &MutHeap<JS<T>>) -> bool {
+        self.get().eq(&other.get())
+    }
+}
+
 /// A holder that provides interior mutability for GC-managed values such as
 /// `JS<T>`, with nullability represented by an enclosing Option wrapper.
 /// Essentially a `Cell<Option<JS<T>>>`, but safer.
@@ -337,6 +343,12 @@ impl<T: HeapGCValue> HeapSizeOf for MutNullableHeap<T> {
     }
 }
 
+impl<T: Reflectable> PartialEq for MutNullableHeap<JS<T>> {
+   fn eq(&self, other: &MutNullableHeap<JS<T>>) -> bool {
+        self.get().eq(&other.get())
+    }
+}
+
 impl<T: Reflectable> LayoutJS<T> {
     /// Returns an unsafe pointer to the interior of this JS object. This is
     /// the only method that be safely accessed from layout. (The fact that