Add a treeChange type to Automation

chrome/browser/resources/chromeos/chromevox/cvox2/background/live_regions_test.extjs

 // 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.
 
 // Include test fixture.
 GEN_INCLUDE(['../../testing/chromevox_next_e2e_test_base.js',
              '../../testing/assert_additions.js']);
 
 GEN_INCLUDE(['../../testing/mock_feedback.js']);
 
@@ skipping 203 matching lines @@
       </script>
     */},
     function(rootNode) {
       var go = rootNode.find({ role: RoleType.button });
       mockFeedback.call(go.doDefault.bind(go))
           .expectCategoryFlushSpeech('Live1')
           .expectCategoryFlushSpeech('Live2');
       mockFeedback.replay();
     });
 });
+
+TEST_F('LiveRegionsTest', 'SilentOnNodeChange', function() {
+  var mockFeedback = this.createMockFeedback();
+  this.runWithLoadedTree(function() {/*!
+    <p>start</p>
+    <button>first</button>
+    <div role="button" id="live" aria-live="polite">
+      hello!
+    </div>
+    <script>
+      var live = document.getElementById('live');
+      var pressed = true;
+      setInterval(function() {
+        live.setAttribute('aria-pressed', pressed);
+        pressed = !pressed;
+      }, 50);
+    </script>
+  */},
+  function(root) {
+    var focusAfterNodeChange = window.setTimeout.bind(window, function() {
+      root.firstChild.nextSibling.focus();
+    }, 1000);
+    mockFeedback.call(focusAfterNodeChange)
+        .expectSpeech('hello!')
+        .expectNextSpeechUtteranceIsNot('hello!')
+        .expectNextSpeechUtteranceIsNot('hello!')       ;
+    mockFeedback.replay();
+  });
+});