[dart2dart] Do not crash on unresolved named constructor

tests/compiler/dart2js/dart_backend_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:uri';
 import 'parser_helper.dart';
 import 'mock_compiler.dart';
 import '../../../sdk/lib/_internal/compiler/compiler.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart' as leg;
 import '../../../sdk/lib/_internal/compiler/implementation/dart_backend/dart_backend.dart';
@@ skipping 674 matching lines @@
   fisk.print('corelib');
   print('local');
 }
 ''';
   var expectedResult = "p_print(x){throw 'fisk';}"
       "main(){print('corelib');p_print('local');}";
   testDart2Dart(src,
       continuation: (String result) { Expect.equals(expectedResult, result); });
 }
 
+testUnresolvedNamedConstructor() {
+  var src = '''
+class A {
+  A() {}
+}
+
+main() {
+  new A();
+  new A.named();
+}
+''';
+  var expectedResult = "class A{A(){}}main(){new A();new p_Unresolved();}";
+  testDart2Dart(src,
+      continuation: (String result) { Expect.equals(expectedResult, result); });
+}
+
 main() {
   testSimpleFileUnparse();
   testTopLevelField();
   testSimpleTopLevelClass();
   testClassWithSynthesizedConstructor();
   testClassWithMethod();
   testExtendsImplements();
   testVariableDefinitions();
   testGetSet();
   testAbstractClass();
@@ skipping 10 matching lines @@
   testClassTypeArgumentBound();
   testDoubleMains();
   testStaticAccessIoLib();
   testLocalFunctionPlaceholder();
   testMinification();
   testClosureLocalsMinified();
   testParametersMinified();
   testDeclarationTypePlaceholders();
   testPlatformLibraryMemberNamesAreFixed();
   testConflictsWithCoreLib();
+  testUnresolvedNamedConstructor();
 }