Revert "Move dart2js from sdk/lib/_internal/compiler to pkg/compiler"

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/util/characters.dart';
+import 'package:compiler/implementation/scanner/scannerlib.dart';
+import 'package:compiler/implementation/util/characters.dart';
 import 'dart:typed_data';
 
 Token scan(List<int> bytes) => new Utf8BytesScanner.fromBytes(bytes).tokenize();
 
 Token scanUTF8(List<int> bytes) {
   int l = bytes.length;
   List<int> stringLiteral = new Uint8List(l + 3);
   stringLiteral[0] = 0x27; // single quote
   stringLiteral[l+1] = 0x27; // single quote
   stringLiteral[l+2] = $EOF;
@@ skipping 46 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.
 }