Bug 1305401 - SimpleOutlineHighlighter checks for node validity before highlighting; r=jdescottes

MozReview-Commit-ID: 8HMcOxyJBj8

--HG--
extra : rebase_source : 066e6eaf756a9f3cc6d04a81dcd4873773942cd3

devtools/server/actors/highlighters/simple-outline.js

@@ -4,8 +4,12 @@
 
 "use strict";
 
-const { installHelperSheet,
-  addPseudoClassLock, removePseudoClassLock } = require("./utils/markup");
+const {
+  installHelperSheet,
+  isNodeValid,
+  addPseudoClassLock,
+  removePseudoClassLock
+} = require("./utils/markup");
 
 // SimpleOutlineHighlighter's stylesheet
 const HIGHLIGHTED_PSEUDO_CLASS = ":-moz-devtools-highlighted";
@@ -41,7 +45,7 @@ SimpleOutlineHighlighter.prototype = {
    * @param {DOMNode} node
    */
   show: function (node) {
-    if (!this.currentNode || node !== this.currentNode) {
+    if (isNodeValid(node) && (!this.currentNode || node !== this.currentNode)) {
       this.hide();
       this.currentNode = node;
       installHelperSheet(node.ownerDocument.defaultView, SIMPLE_OUTLINE_SHEET);