Move computation of RenderLayer::isUnclippedDescendant into CompositingPropertyUpdater

Source/core/rendering/compositing/CompositingPropertyUpdater.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 CompositingPropertyUpdater_h
 #define CompositingPropertyUpdater_h
 
 #include "core/rendering/RenderGeometryMap.h"
 
 namespace WebCore {
 
 class RenderLayer;
 
 class CompositingPropertyUpdater {
+private:
+    struct AncestorInfo {
+        AncestorInfo()
+            : enclosingCompositedLayer(0)
+            , ancestorScrollingLayer(0)
+        {
+        }
+
+        RenderLayer* enclosingCompositedLayer;
+        RenderLayer* ancestorScrollingLayer;
+    };
+
 public:
     explicit CompositingPropertyUpdater(RenderLayer* rootRenderLayer);
     ~CompositingPropertyUpdater();
 
     enum UpdateType {
         DoNotForceUpdate,
         ForceUpdate,
     };
 
-    void updateAncestorDependentProperties(RenderLayer*, UpdateType, RenderLayer* enclosingCompositedLayer);
+    void updateAncestorDependentProperties(RenderLayer*, UpdateType, AncestorInfo = AncestorInfo());
 
 #if !ASSERT_DISABLED
     static void assertNeedsToUpdateAncestorDependantPropertiesBitsCleared(RenderLayer*);
 #endif
 
 private:
     RenderGeometryMap m_geometryMap;
     RenderLayer* m_rootRenderLayer;
 };
 
 } // namespace WebCore
 
 #endif // CompositingPropertyUpdater_h