Dart changes for https://codereview.chromium.org/26571005/

tests/html/custom/document_register_type_extensions_test.dart

Index: tests/html/custom/document_register_type_extensions_test.dart
diff --git a/tests/html/custom/document_register_type_extensions_test.dart b/tests/html/custom/document_register_type_extensions_test.dart
index 3f43234eb8585f47ac84a5c744a002a011e5474b..385887ffbcd14b45be8ab5d31c07c288d0985a64 100644
--- a/tests/html/custom/document_register_type_extensions_test.dart
+++ b/tests/html/custom/document_register_type_extensions_test.dart
@@ -75,8 +75,16 @@ main() {
   group('construction', () {
     setUp(registerTypes);
 
-    test('cannot register twice', () {
-      expect(() => document.register(FooBad.tag, Foo), throws);
+    group('registration', () {
+      test('cannot register twice', () {
+        expect(() => document.register(FooBad.tag, Foo), throws);
+      });
+
+      test('cannot register for non-matching tag', () {
+        expect(() {
+          document.register('x-input-div', Bar, extendsTag: 'div');
+        }, throws);
+      });
     });
 
     group('constructors', () {