Invoke backup element queue via a microtask

components/script/dom/customelementregistry.rs

@@ -29,6 +29,8 @@ use js::conversions::ToJSValConvertible;
 use js::jsapi::{Construct1, IsCallable, IsConstructor, HandleValueArray, HandleObject, MutableHandleValue};
 use js::jsapi::{Heap, JS_GetProperty, JSAutoCompartment, JSContext};
 use js::jsval::{JSVal, NullValue, ObjectValue, UndefinedValue};
+use microtask::Microtask;
+use script_thread::ScriptThread;
 use std::cell::Cell;
 use std::collections::{HashMap, VecDeque};
 use std::ops::Deref;
@@ -532,13 +534,7 @@ impl CustomElementReactionStack {
         self.processing_backup_element_queue.set(BackupElementQueueFlag::Processing);
 
         // Step 4
-        // TODO: Invoke Microtask
-
-        // Step 4.1
-        self.backup_queue.invoke_reactions();
-
-        // Step 4.2
-        self.processing_backup_element_queue.set(BackupElementQueueFlag::NotProcessing);
+        ScriptThread::enqueue_microtask(Microtask::CustomElementReaction);
     }
 
     /// https://html.spec.whatwg.org/multipage/#enqueue-a-custom-element-callback-reaction
@@ -630,6 +626,7 @@ impl ElementQueue {
         while let Some(element) = self.next_element() {
             element.invoke_reactions()
         }
+        self.queue.borrow_mut().clear();
     }
 
     fn next_element(&self) -> Option<Root<Element>> {

components/script/microtask.rs

@@ -15,6 +15,7 @@ use dom::htmlimageelement::ImageElementMicrotask;
 use dom::htmlmediaelement::MediaElementMicrotask;
 use dom::mutationobserver::MutationObserver;
 use msg::constellation_msg::PipelineId;
+use script_thread::ScriptThread;
 use std::cell::Cell;
 use std::mem;
 use std::rc::Rc;
@@ -33,6 +34,7 @@ pub enum Microtask {
     Promise(EnqueuedPromiseCallback),
     MediaElement(MediaElementMicrotask),
     ImageElement(ImageElementMicrotask),
+    CustomElementReaction,
     NotifyMutationObservers,
 }
 
@@ -87,6 +89,9 @@ impl MicrotaskQueue {
                     Microtask::ImageElement(ref task) => {
                         task.handler();
                     },
+                    Microtask::CustomElementReaction => {
+                        ScriptThread::invoke_backup_element_queue();
+                    },
                     Microtask::NotifyMutationObservers => {
                         MutationObserver::notify_mutation_observers();
                     }

components/script/script_thread.rs

@@ -755,6 +755,15 @@ impl ScriptThread {
         })
     }
 
+    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>,