Activate LayerImpl tree with sync+push instead of pointer swap

cc/scrollbar_layer_impl.h

Index: cc/scrollbar_layer_impl.h
diff --git a/cc/scrollbar_layer_impl.h b/cc/scrollbar_layer_impl.h
index 8b194a2dcdc54900aa3d48ef6f9a9130d5251648..19d976315cb5b1b82fb06c18428ca3724f5001a9 100644
--- a/cc/scrollbar_layer_impl.h
+++ b/cc/scrollbar_layer_impl.h
@@ -20,6 +20,10 @@ public:
     static scoped_ptr<ScrollbarLayerImpl> create(LayerTreeImpl* treeImpl, int id);
     virtual ~ScrollbarLayerImpl();
 
+    virtual ScrollbarLayerImpl* toScrollbarLayer() OVERRIDE;
+    int scrollLayerId() const { return m_scrollLayerId; }
+    void setScrollLayerId(int id) { m_scrollLayerId = id; }
+
     ScrollbarGeometryFixedThumb* scrollbarGeometry() const { return m_geometry.get(); }
     void setScrollbarGeometry(scoped_ptr<ScrollbarGeometryFixedThumb>);
     void setScrollbarData(WebKit::WebScrollbar*);
@@ -28,7 +32,6 @@ public:
     void setForeTrackResourceId(ResourceProvider::ResourceId id) { m_foreTrackResourceId = id; }
     void setThumbResourceId(ResourceProvider::ResourceId id) { m_thumbResourceId = id; }
 
-    void setOwningLayer(LayerImpl* owningLayer);
 
     // ScrollbarLayerImplBase implementation.
     virtual float currentPos() const OVERRIDE;
@@ -41,6 +44,9 @@ public:
 
     virtual WebKit::WebScrollbar::Orientation orientation() const OVERRIDE;
 
+    virtual scoped_ptr<LayerImpl> createLayerImpl(LayerTreeImpl*) OVERRIDE;
+    virtual void pushPropertiesTo(LayerImpl*) OVERRIDE;
+
     virtual void appendQuads(QuadSink&, AppendQuadsData&) OVERRIDE;
 
     virtual void didLoseOutputSurface() OVERRIDE;
@@ -93,6 +99,8 @@ private:
     int m_totalSize;
     int m_maximum;
 
+    int m_scrollLayerId;
+
     // Data to implement Scrollbar
     WebKit::WebScrollbar::ScrollbarOverlayStyle m_scrollbarOverlayStyle;
     WebKit::WebVector<WebKit::WebRect> m_tickmarks;