Check that the local frame is not null before instantiating 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 @@
 }
 
 // static
 Worklet* WindowAnimationWorklet::animationWorklet(DOMWindow& window)
 {
     return from(toLocalDOMWindow(window)).animationWorklet();
 }
 
 AnimationWorklet* WindowAnimationWorklet::animationWorklet()
 {
-    if (!m_animationWorklet)
+    if (!m_animationWorklet && frame())
         m_animationWorklet = AnimationWorklet::create(frame());
     return m_animationWorklet.get();
 }
 
 DEFINE_TRACE(WindowAnimationWorklet)
 {
     visitor->trace(m_animationWorklet);
     Supplement<LocalDOMWindow>::trace(visitor);
     DOMWindowProperty::trace(visitor);
 }
 
 } // namespace blink