Update parser so tests pass.

pkg/dart_scanner/lib/scanner.dart

-// Copyright (c) 2016, 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.md file.
-
-library dart_scanner;
-
-import 'src/token.dart' show
-    Token;
-
-import 'src/utf8_bytes_scanner.dart' show
-    Utf8BytesScanner;
-
-abstract class Scanner {
-  List<int> get lineStarts;
-  Token tokenize();
-}
-
-class ScannerResult {
-  final Token tokens;
-  final List<int> lineStarts;
-
-  ScannerResult(this.tokens, this.lineStarts);
-}
-
-ScannerResult scan(List<int> bytes, {bool includeComments: false}) {
-  if (bytes.last != 0) {
-    throw new ArgumentError("[bytes]: the last byte must be null.");
-  }
-  Scanner scanner =
-      new Utf8BytesScanner(bytes, includeComments: includeComments);
-  return new ScannerResult(scanner.tokenize(), scanner.lineStarts);
-}