Implement script-side of callback reactions for Custom Elements V1

third_party/WebKit/LayoutTests/imported/wpt/custom-elements/custom-elements-registry/define-expected.txt

Index: third_party/WebKit/LayoutTests/imported/wpt/custom-elements/custom-elements-registry/define-expected.txt
diff --git a/third_party/WebKit/LayoutTests/imported/wpt/custom-elements/custom-elements-registry/define-expected.txt b/third_party/WebKit/LayoutTests/imported/wpt/custom-elements/custom-elements-registry/define-expected.txt
index 269a077e34332765107314e31c59d1e632e959ed..94afa59265ffc377c831c9cfc1356b7dbdc5be5d 100644
--- a/third_party/WebKit/LayoutTests/imported/wpt/custom-elements/custom-elements-registry/define-expected.txt
+++ b/third_party/WebKit/LayoutTests/imported/wpt/custom-elements/custom-elements-registry/define-expected.txt
@@ -73,7 +73,9 @@ FAIL If extends is spacer, should throw a NotSupportedError assert_throws: funct
 FAIL If extends is elementnametobeunknownelement, should throw a NotSupportedError assert_throws: function "() =>  {
         customElements.define('test-define-extend-' + name, class {}, { extends: name });
       }" did not throw
-PASS If constructor.observedAttributes throws, should rethrow 
+FAIL If constructor.observedAttributes throws, should rethrow assert_throws: function "() => {
+      customElements.define('test-define-observedattributes-rethrow', C);
+    }" did not throw
 PASS If constructor.prototype throws, should rethrow 
 PASS If Type(constructor.prototype) is undefined, should throw a TypeError 
 PASS If Type(constructor.prototype) is string, should throw a TypeError