Add a page to explain earcons in the tutorial

chrome/browser/resources/chromeos/chromevox/cvox2/background/background.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.
 
 /**
  * @fileoverview The entry point for all ChromeVox2 related code for the
  * background page.
  */
 
 goog.provide('Background');
@@ skipping 768 matching lines @@
     if (prevRange && prevRange.start.node) {
       var entered = AutomationUtil.getUniqueAncestors(
           prevRange.start.node, start);
       var embeddedObject = entered.find(function(f) {
         return f.role == RoleType.embeddedObject; });
       if (embeddedObject)
         embeddedObject.focus();
     }
 
     // Next, try to focus the start or end node.
-    if (isFocusableLinkOrControl(start)) {
+    if (!AutomationPredicate.structuralContainer(start) &&
+        start.state.focusable) {
       if (!start.state.focused)
         start.focus();
       return;
-    } else if (isFocusableLinkOrControl(end)) {
+    } else if (!AutomationPredicate.structuralContainer(end) &&
+        end.state.focusable) {
       if (!end.state.focused)
         end.focus();
       return;
     }
 
     // If a common ancestor of |start| and |end| is a link, focus that.
     var ancestor = AutomationUtil.getLeastCommonAncestor(start, end);
     while (ancestor && ancestor.root == start.root) {
       if (isFocusableLinkOrControl(ancestor)) {
         if (!ancestor.state.focused)
@@ skipping 21 matching lines @@
   return new RegExp('^(' + globs.map(function(glob) {
     return glob.replace(/[.+^$(){}|[\]\\]/g, '\\$&')
         .replace(/\*/g, '.*')
         .replace(/\?/g, '.');
   }).join('|') + ')$');
 };
 
 new Background();
 
 });  // goog.scope