Retrieve prototype during custom element construction.

third_party/WebKit/LayoutTests/custom-elements/constructor-context-dies-retrieving-prototype.html

Index: third_party/WebKit/LayoutTests/custom-elements/constructor-context-dies-retrieving-prototype.html
diff --git a/third_party/WebKit/LayoutTests/custom-elements/constructor-context-dies-before-super.html b/third_party/WebKit/LayoutTests/custom-elements/constructor-context-dies-retrieving-prototype.html
similarity index 62%
copy from third_party/WebKit/LayoutTests/custom-elements/constructor-context-dies-before-super.html
copy to third_party/WebKit/LayoutTests/custom-elements/constructor-context-dies-retrieving-prototype.html
index 7b232226ebb579b7739476cd97f5187e14a05750..93f6965c6d059f2570bcf5648ff8d0dcaf76576c 100644
--- a/third_party/WebKit/LayoutTests/custom-elements/constructor-context-dies-before-super.html
+++ b/third_party/WebKit/LayoutTests/custom-elements/constructor-context-dies-retrieving-prototype.html
@@ -15,7 +15,7 @@ function finishJSTest() {}
 
 if (fork()) {
   // The controlling parent frame.
-  let t = async_test('constructor destroys the context before super');
+  let t = async_test('constructor destroys the context retrieving prototype');
   let watcher = new EventWatcher(t, window, 'message');
   watcher.wait_for('message').then(t.step_func((event) => {
     assert_equals(event.data, 'PASS destroyed context');
@@ -26,15 +26,24 @@ if (fork()) {
   }));
 } else {
   // The child frame.
-  class BadConstructor extends HTMLElement {
-    constructor() {
-      destroyContext();
-      super();
-    }
+  let should_destroy = false;
+  let proxy;
+  function BadConstructor() {
+    should_destroy = true;
+    return Reflect.construct(HTMLElement, [], proxy);
   }
-  window.customElements.define('x-x', BadConstructor);
+  proxy = new Proxy(BadConstructor, {
+    get(receiver, name) {
+      if (should_destroy && name == 'prototype') {
+        destroyContext();
+        return 42;
+      }
+      return receiver[name];
+    }
+  });
+  window.customElements.define('x-x', proxy);
   try {
-    new BadConstructor();
+    new proxy();
   } finally {
     done();
   }