[dart2dart] Fix type variables for interfaces and default classes if they are in different libs.

tests/compiler/dart2js/unparser_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("../../../lib/compiler/compiler.dart");
 #import("../../../lib/compiler/implementation/dart_backend/dart_backend.dart");
 #import("../../../lib/compiler/implementation/elements/elements.dart");
@@ skipping 586 matching lines @@
   mylib.main();
 }
 ''';
   var expectedResult =
     'p_main(){}'
     'main(){p_main();}';
   testDart2DartWithLibrary(mainSrc, librarySrc,
       (String result) { Expect.equals(expectedResult, result); });
 }
 
+testInterfaceDefaultAnotherLib() {
+  var librarySrc = '''
+#library('mylib');
+class C<T> {
+  factory I() {}
+}
+''';
+  var mainSrc = '''
+#import('mylib.dart', prefix: 'mylib');
+
+interface I<T> default mylib.C<T> {
+  I();
+}
+
+main() {
+  new I();
+}
+''';
+  var expectedResult =
+    'class C<T>{factory I(){}}'
+    'interface I<T> default C<T>{I();}'
+    'main(){new I();}';
+  testDart2DartWithLibrary(mainSrc, librarySrc,
+      (String result) { Expect.equals(expectedResult, result); });
+}
+
 main() {
   testSignedConstants();
   testGenericTypes();
   testForLoop();
   testEmptyList();
   testClosure();
   testIndexedOperatorDecl();
   testNativeMethods();
   testPrefixIncrements();
   testConstModifier();
@@ skipping 14 matching lines @@
   testDefaultClassWithArgs();
   testClassExtendsWithArgs();
   testStaticInvocation();
   testLibraryGetSet();
   testFieldTypeOutput();
   testDefaultClassNamePlaceholder();
   testFactoryRename();
   testTypeVariablesAreRenamed();
   testClassTypeArgumentBound();
   testDoubleMains();
+  testInterfaceDefaultAnotherLib();
 }