Update dart2js unit tests to dart_parser and dart_scanner.

tests/compiler/dart2js/scanner_offset_length_test.dart

Index: tests/compiler/dart2js/scanner_offset_length_test.dart
diff --git a/tests/compiler/dart2js/scanner_offset_length_test.dart b/tests/compiler/dart2js/scanner_offset_length_test.dart
index 5239f1c738048b0b1f771f916bfedfc3569f5504..a8f01ca3984a5cd97ddc1fd57fe537611d8efac6 100644
--- a/tests/compiler/dart2js/scanner_offset_length_test.dart
+++ b/tests/compiler/dart2js/scanner_offset_length_test.dart
@@ -3,12 +3,10 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import "package:expect/expect.dart";
-import 'package:compiler/src/scanner/string_scanner.dart';
-import 'package:compiler/src/tokens/token.dart';
-import 'package:compiler/src/tokens/token_constants.dart';
+import 'package:dart_scanner/dart_scanner.dart';
 
 Token scan(String text) =>
-    new StringScanner.fromString(text, includeComments: true).tokenize();
+    new StringScanner(text, includeComments: true).tokenize();
 
 check(String text) {
   Token token = scan(text);