Remove owning_id from EffectNode and replace it by an opaque stable_id

cc/blink/web_scrollbar_layer_impl.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/blink/web_scrollbar_layer_impl.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "cc/blink/scrollbar_impl.h"
@@ skipping 57 matching lines @@
   return layer_.get();
 }
 
 void WebScrollbarLayerImpl::SetScrollLayer(blink::WebLayer* layer) {
   cc::Layer* scroll_layer =
       layer ? static_cast<WebLayerImpl*>(layer)->layer() : nullptr;
   layer_->layer()->ToScrollbarLayer()->SetScrollElementId(
       scroll_layer ? scroll_layer->element_id() : cc::ElementId());
 }
 
+// This is not the same as scroll_element_id. scroll_elent_id is the
+// ElementId for the scrolling contents, not the scrollbar itself.
+void WebScrollbarLayerImpl::SetElementId(const cc::ElementId& element_id) {
+  layer_->SetElementId(element_id);
+}
+
 }  // namespace cc_blink