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

pkg/compiler/lib/src/js_emitter/helpers.dart

Index: pkg/compiler/lib/src/js_emitter/helpers.dart
diff --git a/pkg/compiler/lib/src/js_emitter/helpers.dart b/pkg/compiler/lib/src/js_emitter/helpers.dart
deleted file mode 100644
index 017094b71868868de7518f2ac556f5451fdbb024..0000000000000000000000000000000000000000
--- a/pkg/compiler/lib/src/js_emitter/helpers.dart
+++ /dev/null
@@ -1,14 +0,0 @@
-// Copyright (c) 2013, 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.
-
-part of dart2js.js_emitter;
-
-ClassElement computeMixinClass(MixinApplicationElement mixinApplication) {
-  ClassElement mixin = mixinApplication.mixin;
-  while (mixin.isMixinApplication) {
-    mixinApplication = mixin;
-    mixin = mixinApplication.mixin;
-  }
-  return mixin;
-}