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

pkg/compiler/lib/src/dart_backend/dart_backend.dart

Index: pkg/compiler/lib/src/dart_backend/dart_backend.dart
diff --git a/pkg/compiler/lib/src/dart_backend/dart_backend.dart b/pkg/compiler/lib/src/dart_backend/dart_backend.dart
deleted file mode 100644
index 36746b7b724e6964914a559023c02c1c858b8a9b..0000000000000000000000000000000000000000
--- a/pkg/compiler/lib/src/dart_backend/dart_backend.dart
+++ /dev/null
@@ -1,40 +0,0 @@
-// 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.
-
-library dart_backend;
-
-import 'dart:async' show Future;
-import 'dart:math' show max;
-import '../elements/elements.dart';
-import '../dart2jslib.dart';
-import '../dart_types.dart';
-import '../tree/tree.dart';
-import '../cps_ir/cps_ir_nodes.dart' as cps_ir;
-import '../constants/expressions.dart';
-import '../cps_ir/optimizers.dart';
-import 'tree_ir_builder.dart' as tree_builder;
-import 'tree_ir_nodes.dart' as tree_ir;
-import '../util/util.dart';
-import '../mirror_renamer/mirror_renamer.dart';
-import 'logical_rewriter.dart' show LogicalRewriter;
-import 'loop_rewriter.dart' show LoopRewriter;
-import 'copy_propagator.dart' show CopyPropagator;
-import 'statement_rewriter.dart' show StatementRewriter;
-import 'backend_ast_emitter.dart' as backend_ast_emitter;
-import 'backend_ast_nodes.dart' as backend_ast;
-import 'backend_ast_to_frontend_ast.dart' as backend2frontend;
-import '../tracer.dart';
-import '../../compiler.dart' show CompilerOutputProvider;
-
-import '../scanner/scannerlib.dart' show StringToken,
-                                         Keyword,
-                                         OPEN_PAREN_INFO,
-                                         CLOSE_PAREN_INFO,
-                                         SEMICOLON_INFO,
-                                         IDENTIFIER_INFO;
-
-part 'backend.dart';
-part 'renamer.dart';
-part 'placeholder_collector.dart';
-part 'outputter.dart';