auto merge of #2101 : jdm/servo/newroot_rebase, r=Ms2ger

As described in #1764, this strategy uses the following properties:
* DOM members are `JS<T>` types. These cannot be used with being explicitly rooted, but they are required for compiler-derived trace hooks.
* Methods that take DOM type arguments receive `&[mut] JSRef<T>`. These are rooted value references that are cloneable but cannot escape.
* Methods that return DOM values use `Unrooted<T>`. These are values that may or may not be rooted elsewhere, but callers must root them in order to interact with them in any way. One unsoundness hole exists - `Unrooted` values must be rooted ASAP, or there exists the danger that JSAPI calls could be made that could cause the underlying JS value to be GCed.
* All methods are implemented on `JSRef<T>`, enforcing the requirement that all DOM values are rooted for the duration of a method call (with a few exceptions for layout-related code, which cannot root values and therefore interacts with `JS<T>` and `&T` values - this is safe under the assumption that layout code interacts with DOM nodes that are in the tree, therefore rooted, and does not run concurrently with content code)

1 files changed, 21 insertions, 13 deletions

diff --git a/src/components/script/dom/blob.rs b/src/components/script/dom/blob.rs
index 04964af092e..ff5958478b6 100644
--- a/src/components/script/dom/blob.rs
+++ b/src/components/script/dom/blob.rs
@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use dom::bindings::js::JS;
+use dom::bindings::js::{JS, JSRef, Temporary};
 use dom::bindings::utils::{Reflectable, Reflector, reflect_dom_object};
 use dom::bindings::error::Fallible;
 use dom::bindings::codegen::BindingDeclarations::BlobBinding;
@@ -16,38 +16,46 @@ pub struct Blob {
 }
 
 impl Blob {
-    pub fn new_inherited(window: JS<Window>) -> Blob {
+    pub fn new_inherited(window: &JSRef<Window>) -> Blob {
         Blob {
             reflector_: Reflector::new(),
-            window: window
+            window: window.unrooted()
         }
     }
 
-    pub fn new(window: &JS<Window>) -> JS<Blob> {
-        reflect_dom_object(~Blob::new_inherited(window.clone()),
+    pub fn new(window: &JSRef<Window>) -> Temporary<Blob> {
+        reflect_dom_object(~Blob::new_inherited(window),
                            window,
                            BlobBinding::Wrap)
     }
-}
 
-impl Blob {
-    pub fn Constructor(window: &JS<Window>) -> Fallible<JS<Blob>> {
+    pub fn Constructor(window: &JSRef<Window>) -> Fallible<Temporary<Blob>> {
         Ok(Blob::new(window))
     }
+}
+
+pub trait BlobMethods {
+    fn Size(&self) -> u64;
+    fn Type(&self) -> DOMString;
+    fn Slice(&self, _start: Option<i64>, _end: Option<i64>, _contentType: Option<DOMString>) -> Temporary<Blob>;
+    fn Close(&self);
+}
 
-    pub fn Size(&self) -> u64 {
+impl<'a> BlobMethods for JSRef<'a, Blob> {
+    fn Size(&self) -> u64 {
         0
     }
 
-    pub fn Type(&self) -> DOMString {
+    fn Type(&self) -> DOMString {
         ~""
     }
 
-    pub fn Slice(&self, _start: Option<i64>, _end: Option<i64>, _contentType: Option<DOMString>) -> JS<Blob> {
-        Blob::new(&self.window)
+    fn Slice(&self, _start: Option<i64>, _end: Option<i64>, _contentType: Option<DOMString>) -> Temporary<Blob> {
+        let window = self.window.root();
+        Blob::new(&window.root_ref())
     }
 
-    pub fn Close(&self) {}
+    fn Close(&self) {}
 }
 
 impl Reflectable for Blob {