Make full_emitter parts into libraries

pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart

Index: pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart
diff --git a/pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart b/pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart
index 2e0cb0e5d0db55213d7fc102aa03043cf4513a47..a452dd5b7290b24c2c1b0f9299f794a2c438c3b5 100644
--- a/pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart
+++ b/pkg/compiler/lib/src/js_emitter/full_emitter/class_builder.dart
@@ -2,7 +2,17 @@
 // 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.
 
-part of dart2js.js_emitter.full_emitter;
+library dart2js.js_emitter.full_emitter.class_builder;
+
+import '../../elements/elements.dart'
+    show
+    ClassElement,
+    Element;
+import '../../js/js.dart' as jsAst;
+import '../../js/js.dart' show js;
+import '../../js_backend/js_backend.dart'
+    show
+    Namer;
 
 /**
  * A data structure for collecting fragments of a class definition.