Avoid getting stuck when calling focus() on iframe nodes.

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

 // 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.
 
 // Include test fixture.
 GEN_INCLUDE(['../../testing/chromevox_next_e2e_test_base.js',
              '../../testing/assert_additions.js']);
 
 GEN_INCLUDE(['../../testing/mock_feedback.js']);
 
@@ skipping 487 matching lines @@
     assertEquals('classic', global.backgroundObj.mode);
 
     // Now, try refreshing mode (which we call after tab switching) with a range
     // that's not actually focused.
     assertEquals(undefined, root.parent.parent.state.focused);
     global.backgroundObj.setCurrentRange(cursors.Range.fromNode(root.parent.parent));
     global.backgroundObj.refreshMode('');
     assertEquals('classic', global.backgroundObj.mode);
   }.bind(this));
 });
+
+TEST_F('BackgroundTest', 'FocusIframe', function() {
+  this.runWithLoadedTree(  function() {/*!
+    <iframe tabindex=0 src="data:text/html,<p>Inside</p>"></iframe>
+    <button>outside</button>
+  */}, function(root) {
+    var iframe = root.find({role: 'iframe'});
+    var button = root.find({role: 'button'});
+
+    assertEquals('iframe', iframe.role);
+    assertEquals('button', button.role);
+
+    var didFocus = false;
+    iframe.focus = function() {
+      didFocus = true;
+    };
+    var b = global.backgroundObj;
+    b.currentRange_ = cursors.Range.fromNode(button);
+    b.onGotCommand('previousElement');
+    assertFalse(didFocus);
+  }.bind(this));
+});