Add a |skipInitialAncestry| option to tree walking.

chrome/browser/resources/chromeos/chromevox/cvox2/background/tree_walker_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']);
 
 GEN_INCLUDE(['../../testing/snippets.js']);
 
 /**
@@ skipping 118 matching lines @@
 
       // And the reverse.
       // Note that walking into a root is allowed.
       visited = '';
       var node6 = r.lastChild.lastChild;
       assertEquals('6', node6.name);
       walker = new AutomationTreeWalker(node6, 'backward', restrictions);
       while (walker.next().node) {}
       assertEquals('532', visited);
 
+      // Test not visiting ancestors of initial node.
+      var node5 = r.firstChild.firstChild.lastChild;
+      assertEquals('5', node5.name);
+      restrictions.root = function(n) { return n.name == '1'; };
+      restrictions.leaf = function(n) { return !n.firstChild; };
+
+      visited = '';
+      restrictions.skipInitialAncestry = false;
+      walker = new AutomationTreeWalker(node5, 'backward', restrictions);
+      while (walker.next().node) {}
+      assertEquals('4321', visited);
+
+      // 2 and 1 are ancestors; check they get skipped.
+      visited = '';
+      restrictions.skipInitialAncestry = true;
+      walker = new AutomationTreeWalker(node5, 'backward', restrictions);
+      while (walker.next().node) {}
+      assertEquals('43', visited);
+
       // We should skip node 2's subtree.
       walker = new AutomationTreeWalker(
           node2, 'forward', {skipInitialSubtree: true});
       assertEquals(node6, walker.next().node);
     });
 });
 
 TEST_F('AutomationTreeWalkerTest', 'LeafPredicateSymmetry', function() {
   this.runWithLoadedTree(toolbarDoc, function(r) {
     var d = r.root.parent.root;
@@ skipping 22 matching lines @@
         {root: function(node) { return node === r; }});
     assertEquals(r, backwardWalker.next().node);
     assertEquals(null, backwardWalker.next().node);
 
     var forwardWalker =
         new AutomationTreeWalker(r.firstChild.lastChild, 'forward',
             {root: function(node) { return node === r; }});
     assertEquals(null, forwardWalker.next().node);
   });
 });