fix: Prevent color rules from crashing Chrome 66+ #856 (#861)

lib/commons/dom/shadow-elements-from-point.js

@@ -9,11 +9,17 @@
  * @param {Object} [root] Shadow root or document root
  * @return {Array}
  */
-dom.shadowElementsFromPoint = function(nodeX, nodeY, root = document) {
-	return root.elementsFromPoint(nodeX, nodeY)
+dom.shadowElementsFromPoint = function(nodeX, nodeY, root = document, i=0) {
+	if (i > 999) {
+		throw new Error('Infinite loop detected');
+	}
+	return Array.from(root.elementsFromPoint(nodeX, nodeY))
+		// As of Chrome 66, elementFromPoint will return elements from parent trees.
+		// We only want to touch each tree once, so we're filtering out nodes on other trees.
+		.filter(nodes => dom.getRootNode(nodes) === root)
 		.reduce((stack, elm) => {
 			if (axe.utils.isShadowRoot(elm)) {
-				const shadowStack = dom.shadowElementsFromPoint(nodeX, nodeY, elm.shadowRoot);
+				const shadowStack = dom.shadowElementsFromPoint(nodeX, nodeY, elm.shadowRoot, i+1);
 				stack = stack.concat(shadowStack);
 				// filter host nodes which get included regardless of overlap
 				// TODO: refactor multiline overlap checking inside shadow dom