Move dart2jslib parts into separate libraries.

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
index ab6f3887d8f00b7a6fe05d399073154a9fb698f0..bd16595124411d295e6011211d63d52f5977ca2b 100644
--- a/pkg/compiler/lib/src/dart_backend/dart_backend.dart
+++ b/pkg/compiler/lib/src/dart_backend/dart_backend.dart
@@ -6,27 +6,39 @@ library dart_backend;
 
 import 'dart:async' show Future;
 import 'dart:math' show max;
+
+import '../../compiler.dart' show CompilerOutputProvider;
 import '../elements/elements.dart';
 import '../dart2jslib.dart';
-import '../library_loader.dart' show LoadedLibraries;
 import '../dart_types.dart';
-import '../tree/tree.dart';
+import '../diagnostic_listener.dart';
 import '../compile_time_constants.dart';
 import '../constants/constant_system.dart';
 import '../constants/expressions.dart';
 import '../constants/values.dart';
-import '../universe/universe.dart' show UniverseSelector;
-import '../util/util.dart';
+import '../enqueue.dart' show
+    Enqueuer,
+    ResolutionEnqueuer,
+    WorldImpact;
+import '../library_loader.dart' show LoadedLibraries;
+import '../messages.dart' show MessageKind;
 import '../mirror_renamer/mirror_renamer.dart';
+import '../resolution/resolution.dart' show
+    TreeElements,
+    TreeElementMapping;
+import '../scanner/scannerlib.dart' show
+    StringToken,
+    Keyword,
+    OPEN_PAREN_INFO,
+    CLOSE_PAREN_INFO,
+    SEMICOLON_INFO,
+    IDENTIFIER_INFO;
+import '../tree/tree.dart';
+import '../universe/universe.dart' show
+    Selector,
+    UniverseSelector;
+import '../util/util.dart';
 import 'backend_ast_to_frontend_ast.dart' as backend2frontend;
-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';