[worklets] Fixes leak document leak for AnimationWorklet.

third_party/WebKit/Source/modules/compositorworker/WindowAnimationWorklet.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "modules/compositorworker/WindowAnimationWorklet.h"
 
 #include "core/frame/LocalDOMWindow.h"
 #include "core/frame/LocalFrame.h"
 #include "modules/compositorworker/AnimationWorklet.h"
 
@@ skipping 21 matching lines @@
 Worklet* WindowAnimationWorklet::animationWorklet(DOMWindow& window) {
   return from(toLocalDOMWindow(window)).animationWorklet();
 }
 
 AnimationWorklet* WindowAnimationWorklet::animationWorklet() {
   if (!m_animationWorklet && frame())
     m_animationWorklet = AnimationWorklet::create(frame());
   return m_animationWorklet.get();
 }
 
+void WindowAnimationWorklet::frameDestroyed() {
+  m_animationWorklet.clear();
+  DOMWindowProperty::frameDestroyed();
+}
+
 DEFINE_TRACE(WindowAnimationWorklet) {
   visitor->trace(m_animationWorklet);
   Supplement<LocalDOMWindow>::trace(visitor);
   DOMWindowProperty::trace(visitor);
 }
 
 }  // namespace blink