Move dart2jslib parts into separate libraries.

pkg/dart2js_incremental/lib/library_updater.dart

Index: pkg/dart2js_incremental/lib/library_updater.dart
diff --git a/pkg/dart2js_incremental/lib/library_updater.dart b/pkg/dart2js_incremental/lib/library_updater.dart
index bd2188b9340ab85155c457b52cf029b81fe576ee..84df9f2f8fe44f5d673a6da6bc28504523bf4faf 100644
--- a/pkg/dart2js_incremental/lib/library_updater.dart
+++ b/pkg/dart2js_incremental/lib/library_updater.dart
@@ -13,10 +13,7 @@ import 'dart:convert' show
 import 'package:compiler/compiler.dart' as api;
 
 import 'package:compiler/src/dart2jslib.dart' show
-    Compiler,
-    EnqueueTask,
-    MessageKind,
-    Script;
+    Compiler;
 
 import 'package:compiler/src/elements/elements.dart' show
     ClassElement,
@@ -27,6 +24,12 @@ import 'package:compiler/src/elements/elements.dart' show
     STATE_NOT_STARTED,
     ScopeContainerElement;
 
+import 'package:compiler/src/enqueue.dart' show
+    EnqueueTask;
+
+import 'package:compiler/src/messages.dart' show
+    MessageKind;
+
 import 'package:compiler/src/scanner/scannerlib.dart' show
     EOF_TOKEN,
     Listener,
@@ -39,6 +42,9 @@ import 'package:compiler/src/scanner/scannerlib.dart' show
     Scanner,
     Token;
 
+import 'package:compiler/src/script.dart' show
+    Script;
+
 import 'package:compiler/src/io/source_file.dart' show
     CachingUtf8BytesSourceFile,
     SourceFile,