Use IDL union for Timing.duration

Source/core/animation/AnimationNodeTiming.h

 // Copyright 2014 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.
 
 #ifndef AnimationNodeTiming_h
 #define AnimationNodeTiming_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "core/animation/AnimationNode.h"
 #include "wtf/RefCounted.h"
 #include "wtf/text/WTFString.h"
 
 namespace blink {
 
 class DoubleOrString;
 
 class AnimationNodeTiming : public RefCountedWillBeGarbageCollectedFinalized<AnimationNodeTiming>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static PassRefPtrWillBeRawPtr<AnimationNodeTiming> create(AnimationNode* parent);
     double delay();
     double endDelay();
     String fill();
     double iterationStart();
     double iterations();
-    void getDuration(String propertyName, DoubleOrString&);
+    void duration(DoubleOrString&);
     double playbackRate();
     String direction();
     String easing();
 
     void setDelay(double);
     void setEndDelay(double);
     void setFill(String);
     void setIterationStart(double);
     void setIterations(double);
-    bool setDuration(String name, double duration);
+    void setDuration(const DoubleOrString&);
     void setPlaybackRate(double);
     void setDirection(String);
     void setEasing(String);
 
     void trace(Visitor*);
 
 private:
     RefPtrWillBeMember<AnimationNode> m_parent;
     explicit AnimationNodeTiming(AnimationNode*);
 };
 
 } // namespace blink
 
 #endif