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

dart/tests/compiler/dart2js/source_map_d2js_validity_test.dart

 // Copyright (c) 2014, 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:async';
 import 'dart:io';
 
 import 'package:async_helper/async_helper.dart';
 
 import 'source_map_validator_helper.dart';
-import '../../../sdk/lib/_internal/compiler/implementation/dart2js.dart' as entry;
+import 'package:compiler/implementation/dart2js.dart' as entry;
 
 void main() {
   asyncTest(() => createTempDir().then((Directory tmpDir) {
     print('Compiling tests/compiler/dart2js/exit_code_helper.dart');
     Future result =
           entry.internalMain(['tests/compiler/dart2js/exit_code_helper.dart',
                               '-o${tmpDir.path}/out.js',
                               '--library-root=sdk']);
       return result.then((_) {
         Uri uri =
             new Uri.file('${tmpDir.path}/out.js', windows: Platform.isWindows);
         validateSourceMap(uri);
 
         print("Deleting '${tmpDir.path}'.");
         tmpDir.deleteSync(recursive: true);
       });
   }));
-}
+}