Move dart2jslib parts into separate libraries.

pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart

Index: pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart b/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
index d71d685d781349b6e9b89460a8af55c1a73bc1f8..cd09eaafd08eb5b1fb0482c5d8cb5d90d9d55f0c 100644
--- a/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
@@ -28,6 +28,8 @@ import '../../js_backend/js_backend.dart' show
     Namer,
     ConstantEmitter;
 
+import '../../messages.dart' show MessageKind;
+
 import '../../util/util.dart' show
     NO_LOCATION_SPANNABLE;
 
@@ -213,7 +215,7 @@ class ModelEmitter {
     if (compiler.deferredMapUri != null) {
       writeDeferredMap();
     }
-    
+
     // Return the total program size.
     return outputBuffers.values.fold(0, (a, b) => a + b.length);
   }