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

tests/compiler/dart2js/deferred_dont_inline_deferred_constants_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.
 
 // Test that the additional runtime type support is output to the right
 // Files when using deferred loading.
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 import 'memory_source_file_helper.dart';
 import "dart:async";
 
-import 'package:compiler/src/dart2jslib.dart'
+import 'package:compiler/implementation/dart2jslib.dart'
        as dart2js;
 
 class MemoryOutputSink extends EventSink<String> {
   StringBuffer mem = new StringBuffer();
   void add(String event) {
     mem.write(event);
   }
   void addError(String event, [StackTrace stackTrace]) {
     Expect.isTrue(false);
   }
@@ skipping 144 matching lines @@
 """, "lib2.dart": """
 import "main.dart" as main;
 const C4 = "string4";
 const C5 = const main.C(1);
 const C6 = const main.C(2);
 foo() {
   print("lib2");
   main.foo();
 }
 """};