display error message for empty distilled content

components/dom_distiller/core/javascript/dom_distiller_viewer.js

 // 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.
 
 function addToPage(html) {
   var div = document.createElement('div');
   div.innerHTML = html;
   document.getElementById('content').appendChild(div);
 }
 
@@ skipping 47 matching lines @@
         this.colorShuffle = setInterval(function() {
           colorIndex = (colorIndex + 1) % colors.length;
           loader.className = colors[colorIndex];
         }, 600);
       }
     } else if (isLastPage && typeof this.colorShuffle != "undefined") {
       clearInterval(this.colorShuffle);
     }
   };
 }();