Refactor how UseCounter::SyntheticKeyframesInCompositedCSSAnimation is counted

third_party/WebKit/Source/core/animation/Keyframe.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 Keyframe_h
 #define Keyframe_h
 
 #include "core/CoreExport.h"
 #include "core/animation/AnimationEffectReadOnly.h"
 #include "core/animation/EffectModel.h"
@@ skipping 55 matching lines @@
     WTF_MAKE_NONCOPYABLE(PropertySpecificKeyframe);
 
    public:
     virtual ~PropertySpecificKeyframe() {}
     double offset() const { return m_offset; }
     TimingFunction& easing() const { return *m_easing; }
     EffectModel::CompositeOperation composite() const { return m_composite; }
     double underlyingFraction() const {
       return m_composite == EffectModel::CompositeReplace ? 0 : 1;
     }
-    virtual bool isNeutral() const {
-      NOTREACHED();
-      return false;
-    }
+    virtual bool isNeutral() const = 0;
     virtual PassRefPtr<PropertySpecificKeyframe> cloneWithOffset(
         double offset) const = 0;
 
     // FIXME: Remove this once CompositorAnimations no longer depends on
     // AnimatableValues
     virtual bool populateAnimatableValue(
         CSSPropertyID,
         Element&,
         const ComputedStyle& baseStyle,
         const ComputedStyle* parentStyle) const {
@@ skipping 40 matching lines @@
   double m_offset;
   EffectModel::CompositeOperation m_composite;
   RefPtr<TimingFunction> m_easing;
 };
 
 using PropertySpecificKeyframe = Keyframe::PropertySpecificKeyframe;
 
 }  // namespace blink
 
 #endif  // Keyframe_h