servo: Merge #4713 - Return *const T from JS::unsafe_get() (fixes #4712) (from Ms2ger:unsafe_get-const); r=jdm

Source-Repo: https://github.com/servo/servo
Source-Revision: ff8cbff81016c157373c1675f3eee69dd70ae544

servo/components/layout/wrapper.rs

@@ -369,10 +369,8 @@ impl<'ln> TNode<'ln, LayoutElement<'ln>> for LayoutNode<'ln> {
                 None => panic!("not an element")
             };
 
-            let element = &*elem.unsafe_get();
-
             LayoutElement {
-                element: mem::transmute(element),
+                element: &*elem.unsafe_get(),
             }
         }
     }
@@ -719,7 +717,7 @@ impl<'ln> TLayoutNode for ThreadSafeLayoutNode<'ln> {
     }
 
     unsafe fn get<'a>(&'a self) -> &'a Node { // this change.
-        mem::transmute::<*mut Node,&'a Node>(self.get_jsmanaged().unsafe_get())
+        &*self.get_jsmanaged().unsafe_get()
     }
 
     fn first_child(&self) -> Option<ThreadSafeLayoutNode<'ln>> {
@@ -819,7 +817,7 @@ impl<'ln> ThreadSafeLayoutNode<'ln> {
             // FIXME(pcwalton): Workaround until Rust gets multiple lifetime parameters on
             // implementations.
             ThreadSafeLayoutElement {
-                element: &mut *element,
+                element: &*element,
             }
         }
     }

servo/components/script/dom/bindings/js.rs

@@ -311,8 +311,8 @@ impl<T: Reflectable> JS<T> {
     /// Returns an unsafe pointer to the interior of this object. This is the
     /// only method that be safely accessed from layout. (The fact that this is
     /// unsafe is what necessitates the layout wrappers.)
-    pub unsafe fn unsafe_get(&self) -> *mut T {
-        self.ptr as *mut T
+    pub unsafe fn unsafe_get(&self) -> *const T {
+        self.ptr
     }
 
     /// Store an unrooted value in this field. This is safe under the assumption that JS<T>