1 files changed, 67 insertions, 0 deletions
diff --git a/layout/forms/ListMutationObserver.h b/layout/forms/ListMutationObserver.h
new file mode 100644
index 0000000000..8c81077fb6
--- /dev/null
+++ b/layout/forms/ListMutationObserver.h
@@ -0,0 +1,67 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_ListMutationObserver_h
+#define mozilla_ListMutationObserver_h
+
+#include "IDTracker.h"
+#include "nsStubMutationObserver.h"
+
+class nsIFrame;
+
+namespace mozilla {
+
+namespace dom {
+class HTMLInputElement;
+}  // namespace dom
+
+/**
+ * ListMutationObserver
+ * This class invalidates paint for the input element's frame when the content
+ * of its @list changes, or when the @list ID identifies a different element. It
+ * does *not* invalidate paint when the @list attribute itself changes.
+ */
+
+class ListMutationObserver final : public nsStubMutationObserver,
+                                   public dom::IDTracker {
+ public:
+  explicit ListMutationObserver(nsIFrame& aOwningElementFrame,
+                                bool aRepaint = false)
+      : mOwningElementFrame(&aOwningElementFrame) {
+    // We can skip invalidating paint if the frame is still being initialized.
+    Attach(aRepaint);
+  }
+
+  NS_DECL_ISUPPORTS
+
+  // We need to invalidate paint when the list or its options change.
+  NS_DECL_NSIMUTATIONOBSERVER_ATTRIBUTECHANGED
+  NS_DECL_NSIMUTATIONOBSERVER_CHARACTERDATACHANGED
+  NS_DECL_NSIMUTATIONOBSERVER_CONTENTAPPENDED
+  NS_DECL_NSIMUTATIONOBSERVER_CONTENTINSERTED
+  NS_DECL_NSIMUTATIONOBSERVER_CONTENTREMOVED
+
+  /**
+   * Triggered when the same @list ID identifies a different element than
+   * before.
+   */
+  void ElementChanged(dom::Element* aFrom, dom::Element* aTo) override;
+
+  void Attach(bool aRepaint = true);
+  void Detach();
+  void AddObserverIfNeeded();
+  void RemoveObserverIfNeeded(dom::Element* aList);
+  void RemoveObserverIfNeeded() { RemoveObserverIfNeeded(get()); }
+  dom::HTMLInputElement& InputElement() const;
+
+ private:
+  ~ListMutationObserver();
+
+  nsIFrame* mOwningElementFrame;
+};
+}  // namespace mozilla
+
+#endif  // mozilla_ListMutationObserver_h