Remove redundancy in source map entries.

tests/compiler/dart2js/source_map_consistency_helper.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:io';
-import 'dart:convert';
-import 'dart:async';
-
-import 'package:path/path.dart' as path;
-import 'package:expect/expect.dart';
-import 'package:source_maps/source_maps.dart';
-
-checkConsistency(Uri outUri) {
-  print('Accessing $outUri');
-  File sourceFile = new File.fromUri(outUri);
-  Expect.isTrue(sourceFile.existsSync());
-  String mapName = getMapReferenceFromJsOutput(sourceFile.readAsStringSync());
-  Uri mapUri = outUri.resolve(mapName);
-  print('Accessing $mapUri');
-  File mapFile = new File.fromUri(mapUri);
-  Expect.isTrue(mapFile.existsSync());
-  SingleMapping sourceMap = new SingleMapping.fromJson(
-      JSON.decode(mapFile.readAsStringSync()));
-  Expect.equals(outUri, mapUri.resolve(sourceMap.targetUrl));
-  print('Checking sources');
-  sourceMap.urls.forEach((String url) {
-    Expect.isTrue(new File.fromUri(mapUri.resolve(url)).existsSync());
-  });
-}
-
-String getMapReferenceFromJsOutput(String file) {
-  List<String> out = file.split('\n');
-  String mapReference = out[out.length - 3]; // #sourceMappingURL=<url>
-  Expect.isTrue(mapReference.startsWith('//# sourceMappingURL='));
-  return mapReference.substring(mapReference.indexOf('=') + 1);
-}
-
-copyDirectory(Directory sourceDir, Directory destinationDir) {
-  sourceDir.listSync().forEach((FileSystemEntity element) {
-    String newPath = path.join(destinationDir.path,
-                               path.basename(element.path));
-    if (element is File) {
-      element.copySync(newPath);
-    } else if (element is Directory) {
-      Directory newDestinationDir = new Directory(newPath);
-      newDestinationDir.createSync();
-      copyDirectory(element, newDestinationDir);
-    }
-  });
-}
-
-Future<Directory> createTempDir() {
-  return Directory.systemTemp
-      .createTemp('sourceMap_test-')
-      .then((Directory dir) {
-    return dir;
-  });
-}