Fix outerHtml comparisons in document_register_type_extension_test.

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 587e96c9a21a8b2bed3f3e180136518747b7df6e..cacb251a0f77c41911600d9fc205711851692c11 100644
--- a/tests/html/custom/document_register_type_extensions_test.dart
+++ b/tests/html/custom/document_register_type_extensions_test.dart
@@ -63,7 +63,7 @@ main() {
     expect(fooNewed is UnknownElement, isFalse);
 
     var barNewed = new Bar();
-    var barOuterHtml = '<input is="x-bar"></input>';
+    var barOuterHtml = '<input is="x-bar">';
     expect(barNewed.outerHtml, barOuterHtml);
     expect(barNewed is Bar, isTrue);
     expect(barNewed is InputElement, isTrue);
@@ -77,7 +77,7 @@ main() {
     expect(bazNewed is UnknownElement, isFalse);
 
     var quxNewed = new Qux();
-    var quxOuterHtml = '<input is="x-qux"></input>';
+    var quxOuterHtml = '<input is="x-qux">';
     expect(quxNewed.outerHtml, quxOuterHtml);
     expect(quxNewed is Qux, isTrue);
     expect(quxNewed is InputElement, isTrue);