Fix <sky-input> data binding when editing deletes the last char.

sky/framework/sky-input.sky

 <!--
 // 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/framework/sky-element/sky-element.sky" as="SkyElement" />
 
 <sky-element name="sky-input" attributes="value:string">
 <template>
   <style>
@@ skipping 10 matching lines @@
     white-space: nowrap;
     overflow: hidden;
   }
   </style>
   <div id="control" contenteditable on-keydown="handleKeyDown">{{ value }}</div>
 </template>
 <script>
 module.exports = class extends SkyElement {
   shadowRootReady() {
     var control = this.shadowRoot.getElementById('control');
+    var text = control.firstChild;
 
     var observer = new MutationObserver(function() {
+      // contenteditable might remove the text node, but we need to keep it
+      // since that's where the data binding is connected to.
+      if (!text.parentNode)
+        control.appendChild(text);
+      if (this.value == control.textContent)
+        return;
       this.value = control.textContent;
       this.dispatchEvent(new CustomEvent('change', {
         bubbles: true,
       }));
     }.bind(this));
 
     observer.observe(control, {
       subtree: true,
       characterData: true,
       childList: true,
     });
   }
   handleKeyDown(event) {
     // TODO(abarth): You can still get newlines if the user pastes them.
     if (event.keyCode == 0xD)
       event.preventDefault();
   }
 }.register();
 </script>
 </sky-element>