Remove unneeded generation of default constructors from the dart backend.

tests/compiler/dart2js/backend_dart/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 "package:expect/expect.dart";
 import 'dart:async';
 import "package:async_helper/async_helper.dart";
 import '../mock_compiler.dart';
 import '../mock_libraries.dart';
 import 'package:compiler/compiler.dart';
@@ skipping 860 matching lines @@
   throw 'fisk';
 }
 main() {
   print('corelib');
   print_A('local');
 }
 """;
   testDart2Dart(src, expectedResult: expectedResult);
 }
 
-testUnresolvedNamedConstructor() {
+testUnresolvedNamedConstructor1() {

[sigurdm, 2014/09/02 09:14:06]

Maybe it is nicer to keep the class alive with a static:

class A {
  A() {}
  static foo() {}
}

main() {
  A.foo();
  new A.named()
}

==>

class A {
  static foo() {}
}

main() {
  A.foo();
  new unresolved();
}

+  var src = '''
+class A {
+}
+
+main() {
+  new A.named();
+}
+''';
+  var expectedResult = """
+main() {
+  new Unresolved();
+}
+""";
+  testDart2Dart(src, expectedResult: expectedResult);
+}
+
+testUnresolvedNamedConstructor2() {
   var src = '''
 class A {
   A() {}
 }
 
 main() {
   new A();
   new A.named();
 }
 ''';
   var expectedResult = """
 class A {
   A() {}
 }
 main() {
   new A();
-  new Unresolved_A();
+  new Unresolved();
 }
 """;
   testDart2Dart(src, expectedResult: expectedResult);
 }
 
 main() {
   testSimpleFileUnparse();
   testTopLevelField();
   testSimpleTopLevelClass();
   testClassWithSynthesizedConstructor();
@@ skipping 13 matching lines @@
   testClassTypeArgumentBound();
   testDoubleMains();
   testStaticAccessIoLib();
   testLocalFunctionPlaceholder();
   testMinification();
   testClosureLocalsMinified();
   testParametersMinified();
   testDeclarationTypePlaceholders();
   testPlatformLibraryMemberNamesAreFixed();
   testConflictsWithCoreLib();
-  testUnresolvedNamedConstructor();
+  testUnresolvedNamedConstructor1();
+  testUnresolvedNamedConstructor2();
 }

[sigurdm, 2014/09/02 09:14:06]

Could also make a language-test (might already exist):

class A {
  A.named();
  static foo() {}
}

main() {
  A.foo();
  Expect.throws(() => new A());
}