Auto merge of #17614 - cbrewster:custom_element_reactions, r=jdm

Implement custom element reactions

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Initial work for implementing custom element reactions: https://html.spec.whatwg.org/multipage/custom-elements.html#custom-element-reactions

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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 #17433 (github issue number if applicable).

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

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components/script/script_thread.rs

@@ -39,6 +39,7 @@ use dom::bindings::str::DOMString;
 use dom::bindings::structuredclone::StructuredCloneData;
 use dom::bindings::trace::JSTraceable;
 use dom::bindings::utils::WRAP_CALLBACKS;
+use dom::customelementregistry::{CallbackReaction, CustomElementReactionStack};
 use dom::document::{Document, DocumentSource, FocusType, HasBrowsingContext, IsHTMLDocument, TouchEventResult};
 use dom::element::Element;
 use dom::event::{Event, EventBubbles, EventCancelable};
@@ -510,6 +511,9 @@ pub struct ScriptThread {
     /// A list of nodes with in-progress CSS transitions, which roots them for the duration
     /// of the transition.
     transitioning_nodes: DOMRefCell<Vec<JS<Node>>>,
+
+    /// https://html.spec.whatwg.org/multipage/#custom-element-reactions-stack
+    custom_element_reaction_stack: CustomElementReactionStack,
 }
 
 /// In the event of thread panic, all data on the stack runs its destructor. However, there
@@ -742,6 +746,24 @@ impl ScriptThread {
         let _ = window.layout_chan().send(msg);
     }
 
+    pub fn enqueue_callback_reaction(element:&Element, reaction: CallbackReaction) {
+        SCRIPT_THREAD_ROOT.with(|root| {
+            if let Some(script_thread) = root.get() {
+                let script_thread = unsafe { &*script_thread };
+                script_thread.custom_element_reaction_stack.enqueue_callback_reaction(element, reaction);
+            }
+        })
+    }
+
+    pub fn invoke_backup_element_queue() {
+        SCRIPT_THREAD_ROOT.with(|root| {
+            if let Some(script_thread) = root.get() {
+                let script_thread = unsafe { &*script_thread };
+                script_thread.custom_element_reaction_stack.invoke_backup_element_queue();
+            }
+        })
+    }
+
     /// Creates a new script thread.
     pub fn new(state: InitialScriptState,
                port: Receiver<MainThreadScriptMsg>,
@@ -827,6 +849,8 @@ impl ScriptThread {
             docs_with_no_blocking_loads: Default::default(),
 
             transitioning_nodes: Default::default(),
+
+            custom_element_reaction_stack: CustomElementReactionStack::new(),
         }
     }