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, 3 insertions, 0 deletions

diff --git a/src/components/script/dom/xmlhttprequesteventtarget.rs b/src/components/script/dom/xmlhttprequesteventtarget.rs
index 55708581a1d..68d67fab89b 100644
--- a/src/components/script/dom/xmlhttprequesteventtarget.rs
+++ b/src/components/script/dom/xmlhttprequesteventtarget.rs
@@ -37,4 +37,7 @@ impl Reflectable for XMLHttpRequestEventTarget {
     fn mut_reflector<'a>(&'a mut self) -> &'a mut Reflector {
         self.eventtarget.mut_reflector()
     }
+}
+
+pub trait XMLHttpRequestEventTargetMethods {
 }
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