Split scannerlib.dart into several libraries.

tests/compiler/dart2js/scanner_test.dart

 // Copyright (c) 2012, 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 "package:expect/expect.dart";
-import 'package:compiler/src/scanner/scannerlib.dart';
+import 'package:compiler/src/scanner/utf8_bytes_scanner.dart';
+import 'package:compiler/src/scanner/token.dart';
 import 'package:compiler/src/util/characters.dart';
 import 'dart:typed_data';
 
 Token scan(List<int> bytes) {
   List<int> zeroTerminated = new Uint8List(bytes.length + 1);
   zeroTerminated.setRange(0, bytes.length, bytes);
   zeroTerminated[bytes.length] = 0;
   return new Utf8BytesScanner.fromBytes(zeroTerminated).tokenize();
 }
 
@@ skipping 53 matching lines @@
   // "#!"
   token = scan([0x23, 0x21]);
   Expect.equals(token.info, EOF_INFO); // Treated as a comment.
 
   // Regression test for issue 1761.
   // "#! Hello, World!"
   token = scan([0x23, 0x21, 0x20, 0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x2c, 0x20,
                 0x57, 0x6f, 0x72, 0x6c, 0x64, 0x21]);
   Expect.equals(token.info, EOF_INFO); // Treated as a comment.
 }