Use v8::TryCatch in toImplSequence

third_party/WebKit/LayoutTests/custom-elements/spec/define-element.html

Index: third_party/WebKit/LayoutTests/custom-elements/spec/define-element.html
diff --git a/third_party/WebKit/LayoutTests/custom-elements/spec/define-element.html b/third_party/WebKit/LayoutTests/custom-elements/spec/define-element.html
index 729a6cb0d423b5f87635ea4eccfb8e03236511d8..2c8d64587e2c38351ce0b7ca8de3da3e59c7f6d0 100644
--- a/third_party/WebKit/LayoutTests/custom-elements/spec/define-element.html
+++ b/third_party/WebKit/LayoutTests/custom-elements/spec/define-element.html
@@ -410,5 +410,22 @@ test_with_window((w) => {
   assert_false( observedAttributes_invoked, 'Get(constructor, observedAttributes) should not be invoked');
 }, 'Get(constructor, observedAttributes) should not execute if ' +
    'attributeChangedCallback is undefined');
+
+test_with_window((w) => {
+  let attributes = {};
+  attributes[Symbol.iterator] = function*() {
+    throw new TypeError();
+  };
+  class X extends w.HTMLElement {
+    constructor() { super(); }
+    attributeChangedCallback() {}
+    static get observedAttributes() {
+      return attributes;
+    }
+  }
+  assert_throws(TypeError.prototype, () => {
+    w.customElements.define('x-x', X);
+  });
+}, 'Throwing an exception in observedAttributes');
 </script>
 </body>