Activate LayerImpl tree with sync+push instead of pointer swap

cc/scrollbar_layer_impl.cc

Index: cc/scrollbar_layer_impl.cc
diff --git a/cc/scrollbar_layer_impl.cc b/cc/scrollbar_layer_impl.cc
index 81f817df55b8dd65be3fda94b6b88d46b90083ee..4c1ccf7fc830f27501b2f129b944d29d69eb9ae6 100644
--- a/cc/scrollbar_layer_impl.cc
+++ b/cc/scrollbar_layer_impl.cc
@@ -28,6 +28,7 @@ ScrollbarLayerImpl::ScrollbarLayerImpl(LayerTreeImpl* treeImpl, int id)
     , m_currentPos(0)
     , m_totalSize(0)
     , m_maximum(0)
+    , m_scrollLayerId(-1)
     , m_scrollbarOverlayStyle(WebScrollbar::ScrollbarOverlayStyleDefault)
     , m_orientation(WebScrollbar::Horizontal)
     , m_controlSize(WebScrollbar::RegularScrollbar)
@@ -45,6 +46,11 @@ ScrollbarLayerImpl::~ScrollbarLayerImpl()
 {
 }
 
+ScrollbarLayerImpl* ScrollbarLayerImpl::toScrollbarLayer()
+{
+    return this;
+}
+
 void ScrollbarLayerImpl::setScrollbarGeometry(scoped_ptr<ScrollbarGeometryFixedThumb> geometry)
 {
     m_geometry = geometry.Pass();
@@ -101,6 +107,27 @@ gfx::Rect ScrollbarLayerImpl::scrollbarLayerRectToContentRect(const gfx::Rect& l
     return gfx::ToEnclosingRect(contentRect);
 }
 
+scoped_ptr<LayerImpl> ScrollbarLayerImpl::createLayerImpl(LayerTreeImpl* treeImpl)
+{
+    return ScrollbarLayerImpl::create(treeImpl, id()).PassAs<LayerImpl>();
+}
+
+void ScrollbarLayerImpl::pushPropertiesTo(LayerImpl* layer)
+{
+    LayerImpl::pushPropertiesTo(layer);
+
+    ScrollbarLayerImpl* scrollbarLayer = static_cast<ScrollbarLayerImpl*>(layer);
+
+    if (!scrollbarLayer->scrollbarGeometry())
+        scrollbarLayer->setScrollbarGeometry(ScrollbarGeometryFixedThumb::create(make_scoped_ptr(m_geometry->clone())));
+
+    scrollbarLayer->setScrollbarData(&m_scrollbar);
+
+    scrollbarLayer->setBackTrackResourceId(m_backTrackResourceId);
+    scrollbarLayer->setForeTrackResourceId(m_foreTrackResourceId);
+    scrollbarLayer->setThumbResourceId(m_thumbResourceId);
+}
+
 void ScrollbarLayerImpl::appendQuads(QuadSink& quadSink, AppendQuadsData& appendQuadsData)
 {
     bool premultipledAlpha = false;