Move parser and token related libraries into their own subfolder.

pkg/compiler/lib/src/scanner/diet_parser_task.dart

-// Copyright (c) 2015, 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.
-
-library dart2js.parser.diet.task;
-
-import '../common/tasks.dart' show
-    CompilerTask;
-import '../compiler.dart' show
-    Compiler;
-import '../elements/elements.dart' show
-    CompilationUnitElement;
-import '../diagnostics/invariant.dart' show
-    invariant;
-
-import 'listener.dart' show
-    ElementListener,
-    ParserError;
-import 'partial_parser.dart' show
-    PartialParser;
-import 'token.dart' show
-    Token;
-
-class DietParserTask extends CompilerTask {
-  DietParserTask(Compiler compiler) : super(compiler);
-  final String name = 'Diet Parser';
-
-  dietParse(CompilationUnitElement compilationUnit, Token tokens) {
-    measure(() {
-      Function idGenerator = compiler.getNextFreeClassId;
-      ElementListener listener =
-          new ElementListener(compiler, compilationUnit, idGenerator);
-      PartialParser parser = new PartialParser(listener);
-      try {
-        parser.parseUnit(tokens);
-      } on ParserError catch(_) {
-        assert(invariant(compilationUnit, compiler.compilationFailed));
-      }
-    });
-  }
-}