Rationalize Dart mojo and sky package structure

sky/framework/debug/tracing.dart

Index: sky/framework/debug/tracing.dart
diff --git a/sky/framework/debug/tracing.dart b/sky/framework/debug/tracing.dart
deleted file mode 100644
index 557bd2818841b95f55ce76fda55e5348d8e53836..0000000000000000000000000000000000000000
--- a/sky/framework/debug/tracing.dart
+++ /dev/null
@@ -1,12 +0,0 @@
-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-import 'dart:sky' as sky;
-
-dynamic trace(String name, Function f) {
-  sky.window.tracing.begin(name);
-  var result = f();
-  sky.window.tracing.end(name);
-  return result;
-}