4 files changed, 41 insertions, 2 deletions
diff --git a/dom/base/ResizeObserver.cpp b/dom/base/ResizeObserver.cpp
index aefcddd9d..37d940c2b 100644
--- a/dom/base/ResizeObserver.cpp
+++ b/dom/base/ResizeObserver.cpp
@@ -61,7 +61,7 @@ ResizeObserver::Constructor(const GlobalObject& aGlobal,
   }
 
   RefPtr<ResizeObserver> observer = new ResizeObserver(window.forget(), aCb);
-  // TODO: Add the new ResizeObserver to document here in the later patch.
+  document->AddResizeObserver(observer);
 
   return observer.forget();
 }
@@ -86,7 +86,7 @@ ResizeObserver::Observe(Element* aTarget,
     // Per the spec, we need to trigger notification in event loop that
     // contains ResizeObserver observe call even when resize/reflow does
     // not happen.
-    // TODO: Implement the notification scheduling in the later patch.
+    aTarget->OwnerDoc()->ScheduleResizeObserversNotification();
   }
 }
 
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index de793bfab..48d23e325 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -1727,6 +1727,10 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(nsDocument)
       cb.NoteXPCOMChild(mql);
     }
   }
+
+  if (tmp->mResizeObserverController) {
+    tmp->mResizeObserverController->Traverse(cb);
+  }
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 NS_IMPL_CYCLE_COLLECTION_CLASS(nsDocument)
@@ -1832,6 +1836,10 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsDocument)
   }
 
   tmp->mInUnlinkOrDeletion = false;
+
+  if (tmp->mResizeObserverController) {
+    tmp->mResizeObserverController->Unlink();
+  }
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
 nsresult
@@ -12105,6 +12113,24 @@ nsDocument::QuerySelectorAll(const nsAString& aSelector, nsIDOMNodeList **aRetur
   return nsINode::QuerySelectorAll(aSelector, aReturn);
 }
 
+void
+nsDocument::AddResizeObserver(ResizeObserver* aResizeObserver)
+{
+  if (!mResizeObserverController) {
+    mResizeObserverController = MakeUnique<ResizeObserverController>(this);
+  }
+
+  mResizeObserverController->AddResizeObserver(aResizeObserver);
+}
+
+void
+nsDocument::ScheduleResizeObserversNotification() const
+{
+  if (mResizeObserverController) {
+    mResizeObserverController->ScheduleNotification();
+  }
+}
+
 already_AddRefed<nsIDocument>
 nsIDocument::Constructor(const GlobalObject& aGlobal,
                          ErrorResult& rv)
diff --git a/dom/base/nsDocument.h b/dom/base/nsDocument.h
index a319ad13e..220f4152d 100644
--- a/dom/base/nsDocument.h
+++ b/dom/base/nsDocument.h
@@ -59,6 +59,7 @@
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/PendingAnimationTracker.h"
 #include "mozilla/dom/DOMImplementation.h"
+#include "mozilla/dom/ResizeObserverController.h"
 #include "mozilla/dom/ScriptLoader.h"
 #include "mozilla/dom/StyleSheetList.h"
 #include "nsDataHashtable.h"
@@ -1206,6 +1207,10 @@ public:
 
   virtual void UnblockDOMContentLoaded() override;
 
+  void AddResizeObserver(mozilla::dom::ResizeObserver* aResizeObserver) override;
+
+  void ScheduleResizeObserversNotification() const override;
+
 protected:
   friend class nsNodeUtils;
   friend class nsDocumentOnStack;
@@ -1342,6 +1347,9 @@ protected:
 
   nsTArray<nsIObserver*> mCharSetObservers;
 
+  mozilla::UniquePtr<mozilla::dom::ResizeObserverController>
+    mResizeObserverController;
+
   PLDHashTable *mSubDocuments;
 
   // Array of owning references to all children
diff --git a/dom/base/nsIDocument.h b/dom/base/nsIDocument.h
index 29afa5439..760048501 100644
--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -152,6 +152,7 @@ class ProcessingInstruction;
 class Promise;
 class Selection;
 class ScriptLoader;
+class ResizeObserver;
 class StyleSheetList;
 class SVGDocument;
 class SVGSVGElement;
@@ -2874,6 +2875,10 @@ public:
 
   bool ModuleScriptsEnabled();
 
+  virtual void AddResizeObserver(mozilla::dom::ResizeObserver* aResizeObserver) = 0;
+
+  virtual void ScheduleResizeObserversNotification() const = 0;
+
 protected:
   bool GetUseCounter(mozilla::UseCounter aUseCounter)
   {