Serialize zIndex as an integer

Source/core/animation/DoubleStyleInterpolation.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 DoubleStyleInterpolation_h
 #define DoubleStyleInterpolation_h
 
 #include "core/CoreExport.h"
 #include "core/animation/StyleInterpolation.h"
 #include "core/css/CSSPrimitiveValue.h"
 
 namespace blink {
 
 class CORE_EXPORT DoubleStyleInterpolation : public StyleInterpolation {
 public:
     static PassRefPtrWillBeRawPtr<DoubleStyleInterpolation> create(const CSSValue& start, const CSSValue& end, CSSPropertyID id, CSSPrimitiveValue::UnitType type, InterpolationRange clamp)
     {
-        return adoptRefWillBeNoop(new DoubleStyleInterpolation(doubleToInterpolableValue(start), doubleToInterpolableValue(end), id, type == CSSPrimitiveValue::CSS_NUMBER, clamp, false));
+        return adoptRefWillBeNoop(new DoubleStyleInterpolation(doubleToInterpolableValue(start), doubleToInterpolableValue(end), id, type == CSSPrimitiveValue::CSS_NUMBER || type == CSSPrimitiveValue::CSS_INTEGER, clamp, false));
     }
 
     static PassRefPtrWillBeRawPtr<DoubleStyleInterpolation> maybeCreateFromMotionRotation(const CSSValue& start, const CSSValue& end, CSSPropertyID);
 
     static bool canCreateFrom(const CSSValue&);
 
     virtual void apply(StyleResolverState&) const override;
 
     DECLARE_VIRTUAL_TRACE();
 
@@ skipping 12 matching lines @@
     static PassRefPtrWillBeRawPtr<CSSValue> interpolableValueToMotionRotation(InterpolableValue*, bool);
 
     bool m_isNumber;
     InterpolationRange m_clamp;
     bool m_flag;
 
     friend class AnimationDoubleStyleInterpolationTest;
 };
 }
 #endif