[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..8bae2b672a964300881d635f452c2633a34bdc73 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
@@ -43,14 +43,15 @@ Polymer({
 
   /** @private */
   render_: function() {
-    if (!this.ctor)
-      this.templatize(this);
+    // Only initialize once.
+    assert(!this.ctor);
+    // Must have a parent and child in order to add child to parent.
+    assert(this.parentNode && !this.child_);
+    this.templatize(this);
     var parentNode = this.parentNode;
-    if (parentNode && !this.child_) {
-      var instance = this.stamp({});
-      this.child_ = instance.root.firstElementChild;
-      parentNode.insertBefore(instance.root, this);
-    }
+    var instance = this.stamp({});
+    this.child_ = instance.root.firstElementChild;
+    parentNode.insertBefore(instance.root, this);
   },
 
   /**