Make Element::ensureActiveAnimations() return a reference

Source/core/animation/Animation.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 311 matching lines @@
     , m_target(target)
     , m_effect(effect)
     , m_activeInAnimationStack(false)
     , m_priority(priority)
 {
 }
 
 void Animation::didAttach()
 {
     if (m_target)
-        m_target->ensureActiveAnimations()->players().add(player());
+        m_target->ensureActiveAnimations().players().add(player());
 }
 
 void Animation::willDetach()
 {
     if (m_target)
         m_target->activeAnimations()->players().remove(player());
     if (m_activeInAnimationStack)
         clearEffects();
 }
 
 static AnimationStack& ensureAnimationStack(Element* element)
 {
-    return element->ensureActiveAnimations()->defaultStack();
+    return element->ensureActiveAnimations().defaultStack();
 }
 
 void Animation::applyEffects(bool previouslyInEffect)
 {
     ASSERT(isInEffect());
     if (!m_target || !m_effect)
         return;
 
     if (player() && !previouslyInEffect) {
         ensureAnimationStack(m_target.get()).add(this);
@@ skipping 122 matching lines @@
 void Animation::pauseAnimationForTestingOnCompositor(double pauseTime)
 {
     ASSERT(hasActiveAnimationsOnCompositor());
     if (!m_target || !m_target->renderer())
         return;
     for (size_t i = 0; i < m_compositorAnimationIds.size(); ++i)
         CompositorAnimations::instance()->pauseAnimationForTestingOnCompositor(*m_target.get(), m_compositorAnimationIds[i], pauseTime);
 }
 
 } // namespace WebCore