Remove owning_id from EffectNode and replace it by an opaque stable_id

cc/blink/web_scrollbar_layer_impl.cc

Index: cc/blink/web_scrollbar_layer_impl.cc
diff --git a/cc/blink/web_scrollbar_layer_impl.cc b/cc/blink/web_scrollbar_layer_impl.cc
index e966ab05047805d20d8ff4f326114f341f244ec3..5b3d99eb34f8a128a1dab696f449b9415ef1c0d5 100644
--- a/cc/blink/web_scrollbar_layer_impl.cc
+++ b/cc/blink/web_scrollbar_layer_impl.cc
@@ -75,4 +75,10 @@ void WebScrollbarLayerImpl::SetScrollLayer(blink::WebLayer* layer) {
       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