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

tests/compiler/dart2js/maplet_test.dart

 // Copyright (c) 2014, 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/implementation/util/maplet.dart";
+import "package:compiler/src/util/maplet.dart";
 
 main() {
   for (int i = 1; i <= 32; i++) {
     test(i);
   }
 }
 
 test(int size) {
   var maplet = new Maplet();
   for (int i = 0; i < size; i++) {
@@ skipping 50 matching lines @@
 
       for (int j = i; j < k; j++) {
         maplet[j] = '$j';
       }
     }
 
     Expect.equals(size, maplet.length);
     Expect.equals('$i', maplet[i]);
   }
 }