Support slotchange events

third_party/WebKit/LayoutTests/fast/dom/shadow/slotchange-event.html

Index: third_party/WebKit/LayoutTests/fast/dom/shadow/slotchange-event.html
diff --git a/third_party/WebKit/LayoutTests/fast/dom/shadow/v1-slots-api-dynamic.html b/third_party/WebKit/LayoutTests/fast/dom/shadow/slotchange-event.html
similarity index 55%
copy from third_party/WebKit/LayoutTests/fast/dom/shadow/v1-slots-api-dynamic.html
copy to third_party/WebKit/LayoutTests/fast/dom/shadow/slotchange-event.html
index 5d51a088946ff107b36b221d01c36441d1d0a86f..424c0c402c7b1ada63c526462ee1aa996e1e026e 100644
--- a/third_party/WebKit/LayoutTests/fast/dom/shadow/v1-slots-api-dynamic.html
+++ b/third_party/WebKit/LayoutTests/fast/dom/shadow/slotchange-event.html
@@ -18,7 +18,9 @@
 convertTemplatesToShadowRootsWithin(d1);
 removeWhiteSpaceOnlyTextNodes(d1);
 
-test(() => {
+async_test((test) => {
+  var count = 0;
+
   const d1_s1 = d1_shadow.querySelector('slot');
   const d1_d1_s1 = d1_d1_shadow.querySelector('slot');
 
@@ -28,15 +30,34 @@ test(() => {
   assert_array_equals(d1_d1_s1.getAssignedNodes(), [d1_s1]);
   assert_array_equals(d1_d1_s1.getAssignedNodes({'flatten': true}), [d2]);
 
+  d1_s1.addEventListener('slotchange', (e) => {
+    test.step(() => {
+      assert_equals(e.target, d1_s1);
+      assert_array_equals(d1_s1.getAssignedNodes(), [d2, d3]);
+      assert_array_equals(d1_s1.getAssignedNodes({'flatten': true}), [d2, d3]);
+      assert_array_equals(e.scoped, true);
+      count++;
+      // The order when a slotchange event is dispatched in the slots is not guranteed.
+      if (count == 2)
+        test.done();
+    });
+  });
+
+  d1_d1_s1.addEventListener('slotchange', (e) => {
+    test.step(() => {
+      assert_equals(e.target, d1_d1_s1);
+      assert_array_equals(d1_d1_s1.getAssignedNodes(), [d1_s1]);
+      assert_array_equals(d1_d1_s1.getAssignedNodes({'flatten': true}), [d2, d3]);
+      assert_array_equals(e.scoped, true);
+      count++;
+      if (count == 2)
+        test.done();
+    });
+  });
+
   const d3 = document.createElement('div');
   d3.setAttribute('id', 'd3');
   d3.setAttribute('slot', 'd1-s1');
   d1.appendChild(d3);
-
-  assert_array_equals(d1_s1.getAssignedNodes(), [d2, d3]);
-  assert_array_equals(d1_s1.getAssignedNodes({'flatten': true}), [d2, d3]);
-
-  assert_array_equals(d1_d1_s1.getAssignedNodes(), [d1_s1]);
-  assert_array_equals(d1_d1_s1.getAssignedNodes({'flatten': true}), [d2, d3]);
-}, "Distribution should be re-calcualted when assigned nodes of a slot in the parent tree is changed");
+}, "slotchange event should be dispatched.");
 </script>