Run all task spawning through util, to allow for easy hooking.

During debugging, I found it useful to hook all task creation in a
central location, and util::task was the perfect place for it.

r? @pcwalton (or maybe someone else, I'm kinda sending you a bunch of
reviews today because I don't know who better to give them to)

components/script/dom/dedicatedworkerglobalscope.rs

@@ -24,6 +24,7 @@ use script_task::WorkerPostMessage;
 use script_task::StackRootTLS;
 
 use servo_net::resource_task::{ResourceTask, load_whole_resource};
+use servo_util::task::spawn_named_native;
 use servo_util::task_state;
 use servo_util::task_state::{Script, InWorker};
 
@@ -34,8 +35,6 @@ use js::rust::Cx;
 
 use std::rc::Rc;
 use std::ptr;
-use std::task::TaskBuilder;
-use native::task::NativeTaskBuilder;
 use url::Url;
 
 #[dom_struct]
@@ -88,10 +87,7 @@ impl DedicatedWorkerGlobalScope {
                             parent_sender: ScriptChan,
                             own_sender: ScriptChan,
                             receiver: Receiver<ScriptMsg>) {
-        TaskBuilder::new()
-            .native()
-            .named(format!("Web Worker at {}", worker_url.serialize()))
-            .spawn(proc() {
+        spawn_named_native(format!("Web worker for {}", worker_url.serialize()), proc() {
 
             task_state::initialize(Script | InWorker);