Bug 1354211 - Add element.findClosest for finding ancestor by CSS selector. r=automatedtester

Introduces a new function, element.findClosest, that finds the
closest parent node by a CSS selector expression.  This is useful to
find arbitrary elements in the tree above us and is quite possibly
reusable for element.getContainer.

MozReview-Commit-ID: 8rBEepmDdPm

--HG--
extra : rebase_source : 3055d23ce7aeba355de93fdeff52eb4ffdffbc24

testing/marionette/element.js

@@ -655,6 +655,30 @@ function findElements(strategy, selector, document, startNode = undefined) {
   }
 }
 
+/**
+ * Finds the closest parent node of <var>startNode</var> by CSS a
+ * <var>selector</var> expression.
+ *
+ * @param {Node} startNode
+ *     Cyce through <var>startNode</var>'s parent nodes in tree-order
+ *     and return the first match to <var>selector</var>.
+ * @param {string} selector
+ *     CSS selector expression.
+ *
+ * @return {Node=}
+ *     First match to <var>selector</var>, or null if no match was found.
+ */
+element.findClosest = function(startNode, selector) {
+  let node = startNode;
+  while (node.parentNode && node.parentNode.nodeType == ELEMENT_NODE) {
+    node = node.parentNode;
+    if (node.matches(selector)) {
+      return node;
+    }
+  }
+  return null;
+};
+
 /**
  * Determines if <var>obj<var> is an HTML or JS collection.
  *

testing/marionette/test_element.js

@@ -31,6 +31,13 @@ class Element {
 
   get nodeType() { return 1; }
   get ELEMENT_NODE() { return 1; }
+
+  // this is a severely limited CSS selector
+  // that only supports lists of tag names
+  matches(selector) {
+    let tags = selector.split(",");
+    return tags.includes(this.localName);
+  }
 }
 
 class DOMElement extends Element {
@@ -94,6 +101,17 @@ const domFrame = new class extends WindowProxy {
   get parent() { return domWin; }
 };
 
+add_test(function test_findClosest() {
+  equal(element.findClosest(domEl, "foo"), null);
+
+  let foo = new DOMElement("foo");
+  let bar = new DOMElement("bar");
+  bar.parentNode = foo;
+  equal(element.findClosest(bar, "foo"), foo);
+
+  run_next_test();
+});
+
 add_test(function test_isSelected() {
   let checkbox = new DOMElement("input", {type: "checkbox"});
   ok(!element.isSelected(checkbox));