Fix cc scrollbar layer issues with initialization, and use element ids throughout.

cc/layers/solid_color_scrollbar_layer.cc

Index: cc/layers/solid_color_scrollbar_layer.cc
diff --git a/cc/layers/solid_color_scrollbar_layer.cc b/cc/layers/solid_color_scrollbar_layer.cc
index eecf15dbd9b834e3c14f4b34b32cc3b6e612433f..926f4efee38c04da33b36075e48502f485a7ddbb 100644
--- a/cc/layers/solid_color_scrollbar_layer.cc
+++ b/cc/layers/solid_color_scrollbar_layer.cc
@@ -91,10 +91,6 @@ bool SolidColorScrollbarLayer::OpacityCanAnimateOnImplThread() const {
   return true;
 }
 
-bool SolidColorScrollbarLayer::AlwaysUseActiveTreeOpacity() const {
-  return true;
-}
-
 ElementId SolidColorScrollbarLayer::scroll_element_id() const {
   return solid_color_scrollbar_layer_inputs_.scroll_element_id;
 }