Only do full tree sync if tree is actually changed, otherwise just push properties

cc/scrollbar_layer.h

Index: cc/scrollbar_layer.h
diff --git a/cc/scrollbar_layer.h b/cc/scrollbar_layer.h
index 6101dfb66ca98c9e6f3964bfa0477da92b1f82a5..5d1cd06de236873fbb35509538443f580c15aaf2 100644
--- a/cc/scrollbar_layer.h
+++ b/cc/scrollbar_layer.h
@@ -25,6 +25,9 @@ public:
 
     static scoped_refptr<ScrollbarLayer> create(scoped_ptr<WebKit::WebScrollbar>, WebKit::WebScrollbarThemePainter, scoped_ptr<WebKit::WebScrollbarThemeGeometry>, int scrollLayerId);
 
+    int scrollLayerId() const { return m_scrollLayerId; }
+    void setScrollLayerId(int id);
+
     // Layer interface
     virtual void setTexturePriorities(const PriorityCalculator&) OVERRIDE;
     virtual void update(ResourceUpdateQueue&, const OcclusionTracker*, RenderingStats&) OVERRIDE;
@@ -32,9 +35,6 @@ public:
     virtual void pushPropertiesTo(LayerImpl*) OVERRIDE;
     virtual void setContentsScale(float contentsScale) OVERRIDE;
 
-    int scrollLayerId() const { return m_scrollLayerId; }
-    void setScrollLayerId(int id) { m_scrollLayerId = id; }
-
     virtual ScrollbarLayer* toScrollbarLayer() OVERRIDE;
 
 protected: