Move Stylesheet loading and ownership from the layout task into HTML elements

Stylesheets for `HTMLLinkElement`s are now loaded by the resource task, triggered by the element in question. Stylesheets are owned by the elements they're associated with, which can be `HTMLStyleElement`, `HTMLLinkElement`, and `HTMLMetaElement` (for `<meta name="viewport">).

Additionally, the quirks mode stylesheet (just as the user and user agent stylesheets a couple of commits ago), is implemented as a lazy static, loaded once per process and shared between all documents.

This all has various nice consequences:
 - Stylesheet loading becomes a non-blocking operation.
 - Stylesheets are removed when the element they're associated with is removed from the document.
 - It'll be possible to implement the CSSOM APIs that require direct access to the stylesheets (i.e., ~ all of them).
 - Various subtle correctness issues are fixed.

One piece of interesting follow-up work would be to move parsing of external stylesheets to the resource task, too. Right now, it happens in the link element once loading is complete, so blocks the script task. Moving it to the resource task would probably be fairly straight-forward as it doesn't require access to any external state.

1 files changed, 19 insertions, 5 deletions

diff --git a/components/script/dom/htmlstyleelement.rs b/components/script/dom/htmlstyleelement.rs
index d1ac6dcc37b..e225ec33981 100644
--- a/components/script/dom/htmlstyleelement.rs
+++ b/components/script/dom/htmlstyleelement.rs
@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use cssparser::Parser as CssParser;
+use dom::bindings::cell::DOMRefCell;
 use dom::bindings::codegen::Bindings::HTMLStyleElementBinding;
 use dom::bindings::codegen::Bindings::NodeBinding::NodeMethods;
 use dom::bindings::inheritance::Castable;
@@ -10,9 +11,10 @@ use dom::bindings::js::Root;
 use dom::document::Document;
 use dom::element::Element;
 use dom::htmlelement::HTMLElement;
-use dom::node::{ChildrenMutation, Node, window_from_node};
+use dom::node::{ChildrenMutation, Node, document_from_node, window_from_node};
 use dom::virtualmethods::VirtualMethods;
 use layout_interface::{LayoutChan, Msg};
+use std::sync::Arc;
 use style::media_queries::parse_media_query_list;
 use style::stylesheets::{Origin, Stylesheet};
 use util::str::DOMString;
@@ -20,6 +22,7 @@ use util::str::DOMString;
 #[dom_struct]
 pub struct HTMLStyleElement {
     htmlelement: HTMLElement,
+    stylesheet: DOMRefCell<Option<Arc<Stylesheet>>>,
 }
 
 impl HTMLStyleElement {
@@ -27,7 +30,8 @@ impl HTMLStyleElement {
                      prefix: Option<DOMString>,
                      document: &Document) -> HTMLStyleElement {
         HTMLStyleElement {
-            htmlelement: HTMLElement::new_inherited(localName, prefix, document)
+            htmlelement: HTMLElement::new_inherited(localName, prefix, document),
+            stylesheet: DOMRefCell::new(None),
         }
     }
 
@@ -52,13 +56,23 @@ impl HTMLStyleElement {
             Some(a) => String::from(&**a.value()),
             None => String::new(),
         };
+
+        let data = node.GetTextContent().expect("Element.textContent must be a string");
+        let mut sheet = Stylesheet::from_str(&data, url, Origin::Author);
         let mut css_parser = CssParser::new(&mq_str);
         let media = parse_media_query_list(&mut css_parser);
+        sheet.set_media(Some(media));
+        let sheet = Arc::new(sheet);
 
-        let data = node.GetTextContent().expect("Element.textContent must be a string");
-        let sheet = Stylesheet::from_str(&data, url, Origin::Author);
         let LayoutChan(ref layout_chan) = win.layout_chan();
-        layout_chan.send(Msg::AddStylesheet(sheet, media)).unwrap();
+        layout_chan.send(Msg::AddStylesheet(sheet.clone())).unwrap();
+        *self.stylesheet.borrow_mut() = Some(sheet);
+        let doc = document_from_node(self);
+        doc.r().invalidate_stylesheets();
+    }
+
+    pub fn get_stylesheet(&self) -> Option<Arc<Stylesheet>> {
+        self.stylesheet.borrow().clone()
     }
 }