Improve accessibility of Calculator default app.

chrome/common/extensions/docs/examples/apps/calculator/app/view.js

 /**
  * Copyright (c) 2012 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 View(window, model) {
   var view = this;
   var model = model;
   var events = this.defineEvents_();
@@ skipping 70 matching lines @@
     this.addEquation_(display, {operator: operation.operator});
   } else if (!this.updateEquation_(display.lastElementChild, operation)) {
     this.addEquation_(display, operation);
   }
 }
 
 /** @private */
 View.prototype.addEquation_ = function(display, values) {
   // The order of the equation children below makes them stack correctly.
   var equation = this.createDiv_(display, 'equation');
-  equation.appendChild(this.createDiv_(display, 'operand'));
-  equation.appendChild(this.createDiv_(display, 'operator'));
-  equation.appendChild(this.createDiv_(display, 'accumulator'));
+  var operation = this.createDiv_(display, 'operation');
+  operation.appendChild(this.createSpan_(display, 'operator'));
+  operation.appendChild(this.createSpan_(display, 'operand'));
+  equation.appendChild(operation);
+  var accumulator = this.createDiv_(display, 'accumulator');
+  accumulator.setAttribute('aria-hidden', 'true');
+  equation.appendChild(accumulator);
   this.updateEquation_(equation, values);
   display.appendChild(equation).scrollIntoView();
 }
 
 /** @private */
 View.prototype.updateEquation_ = function(equation, values) {
   // Equations which are "finalized" (which have an accumulator value) shouldn't
   // and won't be updated, and this method returns whether an update occurred.
   var accumulator = equation && equation.querySelector('.accumulator');
   var operator = equation && equation.querySelector('.operator');
@@ skipping 14 matching lines @@
     element.textContent = zero ? (value || '0') : (value || '');
   }
 }
 
 /** @private */
 View.prototype.createDiv_ = function(display, classes) {
   var div = display.ownerDocument.createElement('div');
   div.setAttribute('class', classes);
   return div;
 }
+
+/** @private */
+View.prototype.createSpan_ = function(display, classes) {
+  var span = display.ownerDocument.createElement('span');
+  span.setAttribute('class', classes);
+  return span;
+}