Create a common directory of widgets and css.

appengine/chromium_rietveld/new_static/common/cr-button.html

 <!-- Copyright (c) 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. -->
 
 <polymer-element name="cr-button" extends="button" on-keypress="{{ handleKeypress }}">
     <template><style>
             :host {
                 -webkit-user-select: none;
                 background-color: #f5f5f5;
                 background-image: linear-gradient(to bottom, #f5f5f5, #f1f1f1);
@@ skipping 85 matching lines @@
             handleKeypress: function(event) {
                 // Allow space or enter to activate.
                 if (event.keyCode == 32)
                     this.fire("tap");
                 else if (event.keyCode == 13)
                     this.fire("tap");
             },
         });
     </script>
 </ploymer-element>