Rationalize Dart mojo and sky package structure

sky/framework/elements/sky-drawer-header.sky

Index: sky/framework/elements/sky-drawer-header.sky
diff --git a/sky/framework/elements/sky-drawer-header.sky b/sky/framework/elements/sky-drawer-header.sky
deleted file mode 100644
index b680d7ed648a713d753d0b638ed5671e1a7cbf11..0000000000000000000000000000000000000000
--- a/sky/framework/elements/sky-drawer-header.sky
+++ /dev/null
@@ -1,45 +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" />
-<import src="sky-icon.sky" />
-
-<sky-element attributes="icon:string">
-<template>
-  <style>
-    :host {
-      display: flex;
-      flex-direction: column;
-      height: 140px;
-      -webkit-user-select: none;
-      background-color: #E3ECF5;
-      border-bottom: 1px solid #D1D9E1;
-      padding-bottom: 7px;
-      margin-bottom: 8px;
-    }
-    #spacer {
-      flex: 1;
-    }
-    #label {
-      padding: 0 16px;
-      font-family: 'Roboto Medium', 'Helvetica';
-      color: #212121;
-    }
-  </style>
-  <div id="spacer" />
-  <div id="label">
-    <content />
-  </div>
-</template>
-<script>
-import "dart:sky";
-
-@Tagname('sky-drawer-header')
-class SkyDrawerHeader extends SkyElement {
-}
-
-_init(script) => register(script, SkyDrawerHeader);
-</script>
-</sky-element>