Incremental Style Recalc

This patch puts in the initial framework for incremental reflow. Nodes' styles
are no longer recalculated unless the node has changed.

I've been hacking on the general problem of incremental reflow for the past
couple weeks, and I've yet to get a full implementation that actually passes all
the reftests + wikipedia + cnn. Therefore, I'm going to try to land the different
parts of it one by one.

This patch only does incremental style recalc, without incremental flow
construction, inline-size bubbling, reflow, or display lists. Those will be coming
in that order as I finish them.

At least with this strategy, I can land a working version of incremental reflow,
even if not yet complete.

r? @pcwalton

components/net/image/holder.rs

@@ -18,15 +18,16 @@ use url::Url;
 /// A struct to store image data. The image will be loaded once the first time it is requested,
 /// and an Arc will be stored.  Clones of this Arc are given out on demand.
 #[deriving(Clone)]
-pub struct ImageHolder {
+pub struct ImageHolder<NodeAddress> {
     url: Url,
     image: Option<Arc<Box<Image>>>,
     cached_size: Size2D<int>,
-    local_image_cache: Arc<Mutex<LocalImageCache>>,
+    local_image_cache: Arc<Mutex<LocalImageCache<NodeAddress>>>,
 }
 
-impl ImageHolder {
-    pub fn new(url: Url, local_image_cache: Arc<Mutex<LocalImageCache>>) -> ImageHolder {
+impl<NodeAddress: Send> ImageHolder<NodeAddress> {
+    pub fn new(url: Url, local_image_cache: Arc<Mutex<LocalImageCache<NodeAddress>>>)
+               -> ImageHolder<NodeAddress> {
         debug!("ImageHolder::new() {}", url.serialize());
         let holder = ImageHolder {
             url: url,
@@ -60,9 +61,9 @@ impl ImageHolder {
     }
 
     /// Query and update the current image size.
-    pub fn get_size(&mut self) -> Option<Size2D<int>> {
+    pub fn get_size(&mut self, node_address: NodeAddress) -> Option<Size2D<int>> {
         debug!("get_size() {}", self.url.serialize());
-        self.get_image().map(|img| {
+        self.get_image(node_address).map(|img| {
             self.cached_size = Size2D(img.width as int,
                                       img.height as int);
             self.cached_size.clone()
@@ -74,7 +75,7 @@ impl ImageHolder {
         self.image.clone()
     }
 
-    pub fn get_image(&mut self) -> Option<Arc<Box<Image>>> {
+    pub fn get_image(&mut self, node_address: NodeAddress) -> Option<Arc<Box<Image>>> {
         debug!("get_image() {}", self.url.serialize());
 
         // If this is the first time we've called this function, load
@@ -83,7 +84,7 @@ impl ImageHolder {
             let port = {
                 let val = self.local_image_cache.lock();
                 let mut local_image_cache = val;
-                local_image_cache.get_image(&self.url)
+                local_image_cache.get_image(node_address, &self.url)
             };
             match port.recv() {
                 ImageReady(image) => {
@@ -105,5 +106,8 @@ impl ImageHolder {
 
         return result;
     }
-}
 
+    pub fn url(&self) -> &Url {
+        &self.url
+    }
+}