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

tests/compiler/dart2js/patch_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 'dart:async';
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
-import "package:compiler/src/dart2jslib.dart";
-import "package:compiler/src/elements/elements.dart";
-import "package:compiler/src/tree/tree.dart";
+import "package:compiler/implementation/dart2jslib.dart";
+import "package:compiler/implementation/elements/elements.dart";
+import "package:compiler/implementation/tree/tree.dart";
 import "mock_compiler.dart";
 import "mock_libraries.dart";
-import 'package:compiler/src/elements/modelx.dart';
+import 'package:compiler/implementation/elements/modelx.dart';
 
 Future<Compiler> applyPatch(String script, String patch,
                             {bool analyzeAll: false, bool analyzeOnly: false,
                              bool runCompiler: false, String main: ""}) {
   Map<String, String> core = <String, String>{'script': script};
   MockCompiler compiler = new MockCompiler.internal(coreSource: core,
                                                     analyzeAll: analyzeAll,
                                                     analyzeOnly: analyzeOnly);
   var uri = Uri.parse("patch:core");
   compiler.registerSource(uri, "$DEFAULT_PATCH_CORE_SOURCE\n$patch");
@@ skipping 874 matching lines @@
   testPatchNoGetter();
   testPatchNonSetter();
   testPatchNoSetter();
   testPatchNonFunction();
 
   testPatchAndSelector();
 
   testAnalyzeAllInjectedMembers();
   testTypecheckPatchedMembers();
 }