Rationalize Dart mojo and sky package structure

sky/framework/elements/sky-box.sky

Index: sky/framework/elements/sky-box.sky
diff --git a/sky/framework/elements/sky-box.sky b/sky/framework/elements/sky-box.sky
deleted file mode 100644
index 64b6dd4d2e36fb548a3bf59e3bed4344bf55b7c4..0000000000000000000000000000000000000000
--- a/sky/framework/elements/sky-box.sky
+++ /dev/null
@@ -1,53 +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 src="sky-element.sky" />
-
-<sky-element attributes="title:string">
-<template>
-  <style>
-    :host {
-      display: flex;
-      flex-direction: column;
-      border-radius: 4px;
-      border: 1px solid gray;
-      margin: 10px;
-    }
-    #title {
-      text-align: center;
-      font-size: 10px;
-      padding: 8px 8px 4px 8px;
-    }
-    #content {
-      padding: 4px 8px 8px 8px;
-    }
-    div {
-      flex: 1;
-    }
-  </style>
-  <div id="title"></div>
-  <div id="content"><content/></div>
-</template>
-<script>
-import "dart:sky";
-
-@Tagname('sky-box')
-class SkyBox extends SkyElement {
-  Element _title;
-
-  void shadowRootReady() {
-    _title = shadowRoot.getElementById('title');
-    _title.setChild(new Text(title));
-  }
-
-  void titleChanged(String oldValue, String newValue) {
-    if (_title != null)
-      _title.setChild(new Text(newValue));
-  }
-}
-
-_init(script) => register(script, SkyBox);
-</script>
-</sky-element>