Bug 1297784 - Turn performance controls into a React component; r=jsantell

MozReview-Commit-ID: 1R8ky0vW4fH

devtools/client/performance/modules/utils.js

@@ -0,0 +1,21 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+/* globals document */
+
+/**
+ * React components grab the namespace of the element they are mounting to. This function
+ * takes a XUL element, and makes sure to create a properly namespaced HTML element to
+ * avoid React creating XUL elements.
+ *
+ * {XULElement} xulElement
+ * return {HTMLElement} div
+ */
+
+exports.createHtmlMount = function (xulElement) {
+  let htmlElement = document.createElementNS("http://www.w3.org/1999/xhtml", "div");
+  xulElement.appendChild(htmlElement);
+  return htmlElement;
+};