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

tests/compiler/dart2js/indentation_test.dart

 // Copyright (c) 2013, 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/util/util.dart' show Indentation;
+import 'package:compiler/implementation/util/util.dart' show Indentation;
 
 main() {
   Indentation ind = new Indentation();
 
   Expect.stringEquals("", ind.indentation);
 
   ind.indentMore();
   Expect.stringEquals(ind.indentationUnit, ind.indentation);
 
   ind.indentMore();
   Expect.stringEquals(ind.indentationUnit * 2, ind.indentation);
 
   ind.indentBlock(
       () => Expect.stringEquals(ind.indentationUnit * 3, ind.indentation));
   Expect.stringEquals(ind.indentationUnit * 2, ind.indentation);
 
   ind.indentationUnit = "x";
   Expect.stringEquals("xx", ind.indentation);
 
   ind.indentLess();
   Expect.stringEquals("x", ind.indentation);
 
   ind.indentLess();
   Expect.stringEquals("", ind.indentation);
 
   ind.indentMore();
   Expect.stringEquals("x", ind.indentation);
 }