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

cc/scrollbar_layer.cc

Index: cc/scrollbar_layer.cc
diff --git a/cc/scrollbar_layer.cc b/cc/scrollbar_layer.cc
index 09c4e7f0fa75ce8f60e41000ba56e9df7893ec98..9c7ae732c0accee5f01775c524c77d7f72ec8fab 100644
--- a/cc/scrollbar_layer.cc
+++ b/cc/scrollbar_layer.cc
@@ -40,6 +40,15 @@ ScrollbarLayer::~ScrollbarLayer()
 {
 }
 
+void ScrollbarLayer::setScrollLayerId(int id)
+{
+    if (id == m_scrollLayerId)
+        return;
+
+    m_scrollLayerId = id;
+    setNeedsFullTreeSync();
+}
+
 int ScrollbarLayer::maxTextureSize() {
     DCHECK(layerTreeHost());
     return layerTreeHost()->rendererCapabilities().maxTextureSize;