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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components/script/dom/node.rs

@@ -7,6 +7,7 @@
 use app_units::Au;
 use devtools_traits::NodeInfo;
 use document_loader::DocumentLoader;
+use dom::bindings::cell::DOMRefCell;
 use dom::bindings::codegen::Bindings::CharacterDataBinding::CharacterDataMethods;
 use dom::bindings::codegen::Bindings::DocumentBinding::DocumentMethods;
 use dom::bindings::codegen::Bindings::ElementBinding::ElementMethods;
@@ -46,6 +47,7 @@ use dom::htmllinkelement::HTMLLinkElement;
 use dom::htmlmetaelement::HTMLMetaElement;
 use dom::htmlstyleelement::HTMLStyleElement;
 use dom::htmltextareaelement::{HTMLTextAreaElement, LayoutHTMLTextAreaElementHelpers};
+use dom::mutationobserver::RegisteredObserver;
 use dom::nodelist::NodeList;
 use dom::processinginstruction::ProcessingInstruction;
 use dom::range::WeakRangeVec;
@@ -72,7 +74,7 @@ use selectors::matching::matches_selector_list;
 use selectors::parser::SelectorList;
 use servo_url::ServoUrl;
 use std::borrow::ToOwned;
-use std::cell::{Cell, UnsafeCell};
+use std::cell::{Cell, UnsafeCell, RefMut};
 use std::cmp::max;
 use std::default::Default;
 use std::iter;
@@ -138,6 +140,9 @@ pub struct Node {
     /// node is finalized.
     style_and_layout_data: Cell<Option<OpaqueStyleAndLayoutData>>,
 
+    /// Registered observers for this node.
+    mutation_observers: DOMRefCell<Vec<RegisteredObserver>>,
+
     unique_id: UniqueId,
 }
 
@@ -363,6 +368,11 @@ impl Node {
         }
     }
 
+    /// Return all registered mutation observers for this node.
+    pub fn registered_mutation_observers(&self) -> RefMut<Vec<RegisteredObserver>> {
+         self.mutation_observers.borrow_mut()
+    }
+
     /// Dumps the subtree rooted at this node, for debugging.
     pub fn dump(&self) {
         self.dump_indent(0);
@@ -1411,6 +1421,8 @@ impl Node {
 
             style_and_layout_data: Cell::new(None),
 
+            mutation_observers: Default::default(),
+
             unique_id: UniqueId::new(),
         }
     }