[MD settings] handle being detached on cr-lazy-render and settings-idle-render

ui/webui/resources/cr_elements/cr_lazy_render/cr_lazy_render.js

Index: ui/webui/resources/cr_elements/cr_lazy_render/cr_lazy_render.js
diff --git a/ui/webui/resources/cr_elements/cr_lazy_render/cr_lazy_render.js b/ui/webui/resources/cr_elements/cr_lazy_render/cr_lazy_render.js
index 8fac4f477e294249d0918b6df96d7e831cf571eb..81eaef30fd261e917c0b388a3823e5a24c7ea740 100644
--- a/ui/webui/resources/cr_elements/cr_lazy_render/cr_lazy_render.js
+++ b/ui/webui/resources/cr_elements/cr_lazy_render/cr_lazy_render.js
@@ -23,6 +23,11 @@ Polymer({
   /** @private {TemplatizerNode} */
   child_: null,
 
+  /** @override */
+  detached: function() {
+    this.child_ = null;
+  },
+
   /**
    * Stamp the template into the DOM tree synchronously
    * @return {Element} Child element which has been stamped into the DOM tree.