Auto merge of #21111 - gterzian:implement_document_load_cancellation, r=jdm

Implement document load cancellation

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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #19309 fix #21114 fix #21113 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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components/script/dom/bindings/codegen/Bindings.conf

@@ -26,6 +26,10 @@ DOMInterfaces = {
     'weakReferenceable': True,
 },
 
+'EventSource': {
+    'weakReferenceable': True,
+},
+
 #FIXME(jdm): This should be 'register': False, but then we don't generate enum types
 'TestBinding': {},
 

components/script/dom/bindings/weakref.rs

@@ -11,6 +11,7 @@
 //! slot. When all associated `WeakRef` values are dropped, the
 //! `WeakBox` itself is dropped too.
 
+use dom::bindings::cell::DomRefCell;
 use dom::bindings::reflector::DomObject;
 use dom::bindings::root::DomRoot;
 use dom::bindings::trace::JSTraceable;
@@ -286,3 +287,34 @@ impl<'a, T: WeakReferenceable + 'a> Drop for WeakRefEntry<'a, T> {
         *self.index += 1;
     }
 }
+
+#[derive(MallocSizeOf)]
+pub struct DOMTracker<T: WeakReferenceable> {
+    dom_objects: DomRefCell<WeakRefVec<T>>
+}
+
+impl<T: WeakReferenceable> DOMTracker<T> {
+    pub fn new() -> Self {
+        Self {
+            dom_objects: DomRefCell::new(WeakRefVec::new())
+        }
+    }
+
+    pub fn track(&self, dom_object: &T) {
+        self.dom_objects.borrow_mut().push(WeakRef::new(dom_object));
+    }
+
+    pub fn for_each<F: FnMut(DomRoot<T>)>(&self, mut f: F) {
+        self.dom_objects.borrow_mut().update(|weak_ref| {
+            let root = weak_ref.root().unwrap();
+            f(root);
+        });
+    }
+}
+
+#[allow(unsafe_code)]
+unsafe impl<T: WeakReferenceable> JSTraceable for DOMTracker<T> {
+    unsafe fn trace(&self, _: *mut JSTracer) {
+        self.dom_objects.borrow_mut().retain_alive();
+    }
+}