Make PropertyHandle instances const references where possible

third_party/WebKit/Source/core/animation/animatable/AnimatableValueKeyframe.cpp

 // 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.
 
 #include "core/animation/animatable/AnimatableValueKeyframe.h"
 
 #include "core/animation/LegacyStyleInterpolation.h"
 
 namespace blink {
 
@@ skipping 15 matching lines @@
     properties.add(PropertyHandle(*iter.keys()));
   return properties;
 }
 
 PassRefPtr<Keyframe> AnimatableValueKeyframe::clone() const {
   return adoptRef(new AnimatableValueKeyframe(*this));
 }
 
 PassRefPtr<Keyframe::PropertySpecificKeyframe>
 AnimatableValueKeyframe::createPropertySpecificKeyframe(
-    PropertyHandle property) const {
+    const PropertyHandle& property) const {
   return PropertySpecificKeyframe::create(
       offset(), &easing(), propertyValue(property.cssProperty()), composite());
 }
 
 PassRefPtr<Keyframe::PropertySpecificKeyframe>
 AnimatableValueKeyframe::PropertySpecificKeyframe::cloneWithOffset(
     double offset) const {
   return create(offset, m_easing, m_value, m_composite);
 }
 
 PassRefPtr<Interpolation>
 AnimatableValueKeyframe::PropertySpecificKeyframe::createInterpolation(
-    PropertyHandle property,
+    const PropertyHandle& property,
     const Keyframe::PropertySpecificKeyframe& end) const {
   return LegacyStyleInterpolation::create(
       value(), toAnimatableValuePropertySpecificKeyframe(end).value(),
       property.cssProperty());
 }
 
 PassRefPtr<Keyframe::PropertySpecificKeyframe>
 AnimatableValueKeyframe::PropertySpecificKeyframe::neutralKeyframe(
     double offset,
     PassRefPtr<TimingFunction> easing) const {
   return create(offset, std::move(easing), AnimatableValue::neutralValue(),
                 EffectModel::CompositeAdd);
 }
 
 }  // namespace blink