Use reference for FillLayer if possible

Source/core/animation/css/CSSPropertyEquality.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 "config.h"
 #include "core/animation/css/CSSPropertyEquality.h"
 
 #include "core/animation/css/CSSAnimations.h"
 #include "core/rendering/style/DataEquivalency.h"
 #include "core/rendering/style/RenderStyle.h"
 #include "core/rendering/style/ShadowList.h"
 
 namespace WebCore {
 
 namespace {
 
 template <CSSPropertyID property>
-bool fillLayersEqual(const FillLayer* aLayer, const FillLayer* bLayer)
+bool fillLayersEqual(const FillLayer& aLayers, const FillLayer& bLayers)
 {
-    if (aLayer == bLayer)
-        return true;
-    if (!aLayer || !bLayer)
-        return false;
+    const FillLayer* aLayer = &aLayers;
+    const FillLayer* bLayer = &bLayers;
     while (aLayer && bLayer) {
         switch (property) {
         case CSSPropertyBackgroundPositionX:
         case CSSPropertyWebkitMaskPositionX:
             if (aLayer->xPosition() != bLayer->xPosition())
                 return false;
             break;
         case CSSPropertyBackgroundPositionY:
         case CSSPropertyWebkitMaskPositionY:
             if (aLayer->yPosition() != bLayer->yPosition())
@@ skipping 275 matching lines @@
         return a.zIndex() == b.zIndex();
     case CSSPropertyZoom:
         return a.zoom() == b.zoom();
     default:
         ASSERT_NOT_REACHED();
         return true;
     }
 }
 
 }