Make DocumentLoader::timing return a reference

Source/core/animation/AnimationTimeline.cpp

Index: Source/core/animation/AnimationTimeline.cpp
diff --git a/Source/core/animation/AnimationTimeline.cpp b/Source/core/animation/AnimationTimeline.cpp
index 9e2a8009c8ec9528bcdda6615377708785793a9e..26fd46d0effcdb29f6e3f43ff0e2f33959b386b3 100644
--- a/Source/core/animation/AnimationTimeline.cpp
+++ b/Source/core/animation/AnimationTimeline.cpp
@@ -184,7 +184,7 @@ void AnimationTimeline::AnimationTimelineTiming::trace(Visitor* visitor)
 double AnimationTimeline::zeroTime()
 {
     if (!m_zeroTimeInitialized && m_document && m_document->loader()) {
-        m_zeroTime = m_document->loader()->timing()->referenceMonotonicTime();
+        m_zeroTime = m_document->loader()->timing().referenceMonotonicTime();
         m_zeroTimeInitialized = true;
     }
     return m_zeroTime;