Bug 1781046 - Make ResizeObserver::mCallback Variant. r=emilio

So that it can accept a callback function implemented in C++.

Analogous to what D61436 did for DOMIntersectionObserver.

Differential Revision: https://phabricator.services.mozilla.com/D154324

dom/base/ResizeObserver.cpp

@@ -202,14 +202,23 @@ NS_IMPL_CYCLE_COLLECTION_CLASS(ResizeObserver)
 NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(ResizeObserver)
 
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(ResizeObserver)
-  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOwner, mDocument, mCallback,
-                                    mActiveTargets, mObservationMap);
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOwner, mDocument, mActiveTargets,
+                                    mObservationMap);
+  if (tmp->mCallback.is<RefPtr<ResizeObserverCallback>>()) {
+    ImplCycleCollectionTraverse(
+        cb, tmp->mCallback.as<RefPtr<ResizeObserverCallback>>(), "mCallback",
+        0);
+  }
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(ResizeObserver)
   tmp->Disconnect();
-  NS_IMPL_CYCLE_COLLECTION_UNLINK(mOwner, mDocument, mCallback, mActiveTargets,
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mOwner, mDocument, mActiveTargets,
                                   mObservationMap);
+  if (tmp->mCallback.is<RefPtr<ResizeObserverCallback>>()) {
+    ImplCycleCollectionUnlink(
+        tmp->mCallback.as<RefPtr<ResizeObserverCallback>>());
+  }
   NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
@@ -220,6 +229,14 @@ NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(ResizeObserver)
   NS_INTERFACE_MAP_ENTRY(nsISupports)
 NS_INTERFACE_MAP_END
 
+ResizeObserver::ResizeObserver(Document& aDocument, NativeCallback aCallback)
+    : mOwner(aDocument.GetInnerWindow()),
+      mDocument(&aDocument),
+      mCallback(aCallback) {
+  MOZ_ASSERT(mOwner, "Need a non-null owner window");
+  MOZ_ASSERT(mDocument == mOwner->GetExtantDoc());
+}
+
 already_AddRefed<ResizeObserver> ResizeObserver::Constructor(
     const GlobalObject& aGlobal, ResizeObserverCallback& aCb,
     ErrorResult& aRv) {
@@ -383,8 +400,13 @@ uint32_t ResizeObserver::BroadcastActiveObservations() {
     }
   }
 
-  RefPtr<ResizeObserverCallback> callback(mCallback);
-  callback->Call(this, entries, *this);
+  if (mCallback.is<RefPtr<ResizeObserverCallback>>()) {
+    RefPtr<ResizeObserverCallback> callback(
+        mCallback.as<RefPtr<ResizeObserverCallback>>());
+    callback->Call(this, entries, *this);
+  } else {
+    mCallback.as<NativeCallback>()(entries, *this);
+  }
 
   mActiveTargets.Clear();
   mHasSkippedTargets = false;

dom/base/ResizeObserver.h

@@ -115,13 +115,19 @@ class ResizeObservation final : public LinkedListElement<ResizeObservation> {
  * https://drafts.csswg.org/resize-observer/#api
  */
 class ResizeObserver final : public nsISupports, public nsWrapperCache {
+  using NativeCallback = void (*)(
+      const Sequence<OwningNonNull<ResizeObserverEntry>>&, ResizeObserver&);
+  ResizeObserver(Document& aDocument, NativeCallback aCallback);
+
  public:
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(ResizeObserver)
 
   ResizeObserver(nsCOMPtr<nsPIDOMWindowInner>&& aOwner, Document* aDocument,
                  ResizeObserverCallback& aCb)
-      : mOwner(std::move(aOwner)), mDocument(aDocument), mCallback(&aCb) {
+      : mOwner(std::move(aOwner)),
+        mDocument(aDocument),
+        mCallback(RefPtr<ResizeObserverCallback>(&aCb)) {
     MOZ_ASSERT(mOwner, "Need a non-null owner window");
     MOZ_ASSERT(mDocument, "Need a non-null doc");
     MOZ_ASSERT(mDocument == mOwner->GetExtantDoc());
@@ -180,7 +186,7 @@ class ResizeObserver final : public nsISupports, public nsWrapperCache {
   nsCOMPtr<nsPIDOMWindowInner> mOwner;
   // The window's document at the time of ResizeObserver creation.
   RefPtr<Document> mDocument;
-  RefPtr<ResizeObserverCallback> mCallback;
+  Variant<RefPtr<ResizeObserverCallback>, NativeCallback> mCallback;
   nsTArray<RefPtr<ResizeObservation>> mActiveTargets;
   // The spec uses a list to store the skipped targets. However, it seems what
   // we want is to check if there are any skipped targets (i.e. existence).