servo: Merge #17672 - Use boxed slice instead of vec for FuntionTimerCallback (from sadmansk:heap_in_box); r=jdm

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Added `fn trace()` implementation for `Box<[T]>` type, and change FunctionTimerCallback to store boxed slices for heap values instead of Vector.

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #17611

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- [x] These changes do not require tests

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Source-Repo: https://github.com/servo/servo
Source-Revision: 749891e48ec6faa14447b299c48887754872e497

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : c2b1dee39ef62fd78b951b6c02eb0e1df9ede355

servo/components/script/dom/bindings/trace.rs

@@ -177,6 +177,14 @@ unsafe impl<T: JSTraceable + ?Sized> JSTraceable for Box<T> {
     }
 }
 
+unsafe impl<T: JSTraceable> JSTraceable for [T] {
+    unsafe fn trace(&self, trc: *mut JSTracer) {
+        for e in self.iter() {
+            e.trace(trc);
+        }
+    }
+}
+
 unsafe impl<T: JSTraceable + Copy> JSTraceable for Cell<T> {
     unsafe fn trace(&self, trc: *mut JSTracer) {
         self.get().trace(trc)

servo/components/script/timers.rs

@@ -350,7 +350,7 @@ pub enum TimerCallback {
 #[derive(JSTraceable, Clone)]
 enum InternalTimerCallback {
     StringTimerCallback(DOMString),
-    FunctionTimerCallback(Rc<Function>, Rc<Vec<Heap<JSVal>>>),
+    FunctionTimerCallback(Rc<Function>, Rc<Box<[Heap<JSVal>]>>),
 }
 
 impl HeapSizeOf for InternalTimerCallback {
@@ -392,7 +392,7 @@ impl JsTimers {
                 for (i, item) in arguments.iter().enumerate() {
                     args.get_mut(i).unwrap().set(item.get());
                 }
-                InternalTimerCallback::FunctionTimerCallback(function, Rc::new(args))
+                InternalTimerCallback::FunctionTimerCallback(function, Rc::new(args.into_boxed_slice()))
             }
         };