Make Element::ensureActiveAnimations() return a reference

Source/core/dom/Element.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2013 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 486 matching lines @@
     PassRefPtr<RenderStyle> styleForRenderer();
 
     bool hasID() const;
     bool hasClass() const;
     const SpaceSplitString& classNames() const;
 
     IntSize savedLayerScrollOffset() const;
     void setSavedLayerScrollOffset(const IntSize&);
 
     ActiveAnimations* activeAnimations() const;
-    ActiveAnimations* ensureActiveAnimations();
+    ActiveAnimations& ensureActiveAnimations();
     bool hasActiveAnimations() const;
 
     InputMethodContext* inputMethodContext();
     bool hasInputMethodContext() const;
 
     void setPrefix(const AtomicString&, ExceptionState&);
 
     void synchronizeAttribute(const AtomicString& localName) const;
 
     MutableStylePropertySet* ensureMutableInlineStyle();
@@ skipping 341 matching lines @@
 }
 
 inline bool isShadowHost(const Element* element)
 {
     return element && element->shadow();
 }
 
 } // namespace
 
 #endif