Update imports to use package:compiler and package:try.

dart/tests/compiler/dart2js/union_type_test.dart

 // Copyright (c) 2013, 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 "package:async_helper/async_helper.dart";
 import "compiler_helper.dart";
 import "parser_helper.dart";
 
-import "../../../sdk/lib/_internal/compiler/implementation/types/types.dart";
-import "../../../sdk/lib/_internal/compiler/implementation/dart_types.dart";
+import "package:compiler/implementation/types/types.dart";
+import "package:compiler/implementation/dart_types.dart";
 
 main() {
   asyncTest(() => MockCompiler.create((MockCompiler compiler) {
     compiler.intClass.ensureResolved(compiler);
     compiler.stringClass.ensureResolved(compiler);
 
     FlatTypeMask mask1 =
         new FlatTypeMask.exact(compiler.intClass);
     FlatTypeMask mask2 =
         new FlatTypeMask.exact(compiler.stringClass);
     UnionTypeMask union1 = mask1.nonNullable().union(mask2, compiler);
     UnionTypeMask union2 = mask2.nonNullable().union(mask1, compiler);
     Expect.equals(union1, union2);
   }));
 }