Change get_attr() to get_attr_val_for_layout().

The old code was used by both layout and script, but was erroneously
borrowing for the layout case (which causes parallelism
problems). script now uses only `value_ref()` or `get_attribute()`, and
layout now has its own unsafe version that dances around the borrows of
`@mut Attr`.

src/components/script/dom/attr.rs

@@ -65,6 +65,10 @@ impl Attr {
         util::swap(&mut self.value, &mut value);
         value
     }
+
+    pub fn value_ref<'a>(&'a self) -> &'a str {
+        self.value.as_slice()
+    }
 }
 
 impl Attr {

src/components/script/dom/document.rs

@@ -366,7 +366,7 @@ impl Document {
 
     pub fn GetElementsByName(&self, name: DOMString) -> @mut HTMLCollection {
         self.createHTMLCollection(|elem|
-            elem.get_attr(Null, "name").is_some() && eq_slice(elem.get_attr(Null, "name").unwrap(), name))
+            elem.get_attribute(Null, "name").is_some() && eq_slice(elem.get_attribute(Null, "name").unwrap().value_ref(), name))
     }
 
     pub fn createHTMLCollection(&self, callback: |elem: &Element| -> bool) -> @mut HTMLCollection {
@@ -456,9 +456,9 @@ fn foreach_ided_elements(root: &AbstractNode, callback: |&DOMString, &AbstractNo
         }
 
         node.with_imm_element(|element| {
-            match element.get_attr(Null, "id") {
+            match element.get_attribute(Null, "id") {
                 Some(id) => {
-                    callback(&id.to_str(), &node);
+                    callback(&id.Value(), &node);
                 }
                 None => ()
             }

src/components/script/dom/element.rs

@@ -23,8 +23,10 @@ use layout_interface::{ContentBoxesResponse, ContentChangedDocumentDamage};
 use layout_interface::{MatchSelectorsDocumentDamage};
 use style;
 
-use std::str::eq;
 use std::ascii::StrAsciiExt;
+use std::cast;
+use std::str::eq;
+use std::unstable::raw::Box;
 
 pub struct Element {
     node: Node,
@@ -155,9 +157,19 @@ impl Element {
         }).map(|&x| x)
     }
 
-    // FIXME(pcwalton): This is kind of confusingly named relative to the above...
-    pub fn get_attr(&self, namespace: Namespace, name: &str) -> Option<~str> {
-        self.get_attribute(namespace, name).map(|attr| attr.value.clone())
+    pub unsafe fn get_attr_val_for_layout(&self, namespace: Namespace, name: &str) 
+                                          -> Option<&'static str> {
+        // FIXME: only case-insensitive in the HTML namespace (as opposed to SVG, etc.)
+        let name = name.to_ascii_lower();
+        self.attrs.iter().find(|attr: & &@mut Attr| {
+            // unsafely avoid a borrow because this is accessed by many tasks
+            // during parallel layout
+            let attr: ***Box<Attr> = cast::transmute(attr);
+            name == (***attr).data.local_name && (***attr).data.namespace == namespace
+       }).map(|attr| {
+            let attr: **Box<Attr> = cast::transmute(attr);
+            cast::transmute((**attr).data.value.as_slice())
+        })
     }
 
     pub fn set_attr(&mut self, abstract_self: AbstractNode, name: DOMString, value: DOMString)
@@ -352,8 +364,8 @@ impl Element {
     }
 
     pub fn get_string_attribute(&self, name: &str) -> DOMString {
-        match self.get_attr(Null, name) {
-            Some(x) => x,
+        match self.get_attribute(Null, name) {
+            Some(x) => x.Value(),
             None => ~""
         }
     }
@@ -390,7 +402,7 @@ impl Element {
     }
 
     pub fn GetAttribute(&self, name: DOMString) -> Option<DOMString> {
-        self.get_attr(Null, name).map(|s| s.to_owned())
+        self.get_attribute(Null, name).map(|s| s.Value())
     }
 
     pub fn GetAttributeNS(&self, namespace: Option<DOMString>, local_name: DOMString) -> Option<DOMString> {

src/components/script/dom/htmldocument.rs

@@ -11,7 +11,6 @@ use dom::window::Window;
 
 use js::jsapi::JSTracer;
 use std::str::eq_slice;
-use style::TElement;
 
 pub struct HTMLDocument {
     parent: Document
@@ -46,7 +45,7 @@ impl HTMLDocument {
     pub fn Links(&self) -> @mut HTMLCollection {
         self.parent.createHTMLCollection(|elem|
             (eq_slice(elem.tag_name, "a") || eq_slice(elem.tag_name, "area"))
-            && elem.get_attr(Null, "href").is_some())
+            && elem.get_attribute(Null, "href").is_some())
     }
 
     pub fn Forms(&self) -> @mut HTMLCollection {
@@ -59,7 +58,7 @@ impl HTMLDocument {
 
     pub fn Anchors(&self) -> @mut HTMLCollection {
         self.parent.createHTMLCollection(|elem|
-            eq_slice(elem.tag_name, "a") && elem.get_attr(Null, "name").is_some())
+            eq_slice(elem.tag_name, "a") && elem.get_attribute(Null, "name").is_some())
     }
 
     pub fn Applets(&self) -> @mut HTMLCollection {

src/components/script/dom/htmlimageelement.rs

@@ -15,7 +15,6 @@ use layout_interface::{ContentBoxQuery, ContentBoxResponse};
 use servo_net::image_cache_task;
 use servo_net::image_cache_task::ImageCacheTask;
 use servo_util::url::make_url;
-use style::TElement;
 
 pub struct HTMLImageElement {
     htmlelement: HTMLElement,
@@ -41,7 +40,7 @@ impl HTMLImageElement {
     /// prefetching the image. This method must be called after `src` is changed.
     pub fn update_image(&mut self, image_cache: ImageCacheTask, url: Option<Url>) {
         let elem = &mut self.htmlelement.element;
-        let src_opt = elem.get_attr(Null, "src").map(|x| x.to_str());
+        let src_opt = elem.get_attribute(Null, "src").map(|x| x.Value());
         match src_opt {
             None => {}
             Some(src) => {