Make slotchange events bubble

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

Index: third_party/WebKit/LayoutTests/shadow-dom/slotchange.html
diff --git a/third_party/WebKit/LayoutTests/shadow-dom/slotchange.html b/third_party/WebKit/LayoutTests/shadow-dom/slotchange.html
index 6dcd9a9a184162ab4e9cda8152d50e52eb73de3d..7747bdc5b4701069f82a2f970256d75f4790ad77 100644
--- a/third_party/WebKit/LayoutTests/shadow-dom/slotchange.html
+++ b/third_party/WebKit/LayoutTests/shadow-dom/slotchange.html
@@ -5,7 +5,7 @@
 
 <div id="test1">
   <div id="host1">
-    <template data-mode="open">
+    <template id="shadowroot" data-mode="open">
       <slot id="s1" name="slot1"></slot>
     </template>
     <div id="c1" slot="slot1"></div>
@@ -30,6 +30,21 @@ async_test((test) => {
   let n = createTestTree(test1);
   removeWhiteSpaceOnlyTextNodes(n.test1);
 
+  n.shadowroot.addEventListener('slotchange', test.step_func_done((e) => {
+    assert_true(event.bubbles, 'A slotchange should be a bubbling event');
+    assert_false(event.composed, 'A slotchange should be a non-composed event')
+    assert_equals(event.target, n.s1);
+  }))
+
+  let d1 = document.createElement('div');
+  d1.setAttribute('slot', 'slot1');
+  n.host1.appendChild(d1);
+}, 'A slotchange event shoud be a bubble, non-composed event.');
+
+async_test((test) => {
+  let n = createTestTree(test1);
+  removeWhiteSpaceOnlyTextNodes(n.test1);
+
   doneIfSlotChange([n.s1], test);
 
   let d1 = document.createElement('div');