Auto merge of #16883 - jdm:mutationobserver, r=jdm

Mutation Observer API

Rebased from #16668.

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix (partially) #6633
- [X] There are tests for these changes

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1 files changed, 5 insertions, 0 deletions

diff --git a/components/script/microtask.rs b/components/script/microtask.rs
index da04d1ed6ab..7fadf111ddb 100644
--- a/components/script/microtask.rs
+++ b/components/script/microtask.rs
@@ -11,6 +11,7 @@ use dom::bindings::cell::DOMRefCell;
 use dom::bindings::codegen::Bindings::PromiseBinding::PromiseJobCallback;
 use dom::bindings::js::Root;
 use dom::globalscope::GlobalScope;
+use dom::mutationobserver::MutationObserver;
 use msg::constellation_msg::PipelineId;
 use std::cell::Cell;
 use std::mem;
@@ -28,6 +29,7 @@ pub struct MicrotaskQueue {
 #[derive(JSTraceable, HeapSizeOf)]
 pub enum Microtask {
     Promise(EnqueuedPromiseCallback),
+    NotifyMutationObservers,
 }
 
 /// A promise callback scheduled to run during the next microtask checkpoint (#4283).
@@ -71,6 +73,9 @@ impl MicrotaskQueue {
                             let _ = job.callback.Call_(&*target, ExceptionHandling::Report);
                         }
                     }
+                    Microtask::NotifyMutationObservers => {
+                        MutationObserver::notify_mutation_observers();
+                    }
                 }
             }
         }