Move dart2jslib parts into separate libraries.

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

 // Copyright (c) 2011, 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 scanner;
 
 import 'dart:collection' show IterableBase, HashSet;
 
 import '../dart_types.dart' show DynamicType;
+import '../diagnostic_listener.dart';
 import '../elements/elements.dart';
 
 import '../elements/modelx.dart' show
     BaseFunctionElementX,
     ClassElementX,
     CompilationUnitElementX,
     ConstructorElementX,
     DeclarationSite,
     ElementX,
     EnumClassElementX,
     FieldElementX,
     GetterElementX,
     MethodElementX,
     LibraryElementX,
     MetadataAnnotationX,
     MixinApplicationElementX,
     SetterElementX,
     TypedefElementX,
     VariableElementX,
     VariableList;
 
 import '../elements/visitor.dart'
     show ElementVisitor;
 import '../dart2jslib.dart';
+import '../messages.dart';
 import '../native/native.dart' as native;
 import '../string_validator.dart';
+import '../script.dart';
 import '../tree/tree.dart';
 import '../util/characters.dart';
 import '../util/util.dart';
 import '../io/source_file.dart' show SourceFile, Utf8BytesSourceFile;
 import 'dart:convert' show UTF8, UNICODE_BOM_CHARACTER_RUNE;
 
 part 'class_element_parser.dart';
 part 'keyword.dart';
 part 'listener.dart';
 part 'parser.dart';
 part 'parser_task.dart';
 part 'partial_parser.dart';
 part 'scanner.dart';
 part 'scanner_task.dart';
 part 'array_based_scanner.dart';
 part 'utf8_bytes_scanner.dart';
 part 'string_scanner.dart';
 part 'token.dart';