Add initial SkyElement & city-list example

sky/framework/sky-element/sky-element.sky

+<!--
+// Copyright 2014 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.
+-->
+<link rel="import" href="TemplateBinding.sky" />
+
+<script>
+(function(global) {
+  'use strict';
+
+  var Base = {
+
+    __proto__: HTMLElement.prototype,
+
+    register: function() {
+      // |this| is prototype
+      var template = document.currentScript.previousElementSibling;
+      if (template && template.localName == 'template') {
+        this.template_ = template;
+      }
+    },
+
+    createdCallback: function() {
+    },
+
+    attachedCallback: function() {
+      var shadow = this.createShadowRoot();
+      shadow.appendChild(this.template_.createInstance(this));
+      this.attached();
+    },
+
+    attached: function() {
+      // override
+    },
+
+    dettachedCallback: function() {
+      this.dettached();
+    },
+
+    dettached: function() {
+      // override
+    },
+
+    attributeChangedCallback: function(attrName, oldValue, newValue) {
+      // reserved for canonical behavior
+      this.attributeChanged(attrName, oldValue, newValue);
+    },
+
+    attributeChanged: function(attrName, oldValue, newValue) {
+      // override
+    }
+  };
+
+  function SkyElement(prototype) {
+    prototype.__proto__ = Base;
+    document.registerElement(prototype.name, { prototype: prototype });
+    prototype.register();
+  };
+
+  module.exports = SkyElement;
+})(this);
+</script>