Expose br tag in AX Tree as ROLE_SYSTEM_WHITESPACE.

chrome/common/extensions/api/automation.idl

 // 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.
 
 // The <code>chrome.automation</code> API allows developers to access the
 // automation (accessibility) tree for the browser. The tree resembles the DOM
 // tree, but only exposes the <em>semantic</em> structure of a page. It can be
 // used to programmatically interact with a page by examining names, roles, and
 // states, listening for events, and performing actions on nodes.
 [nocompile] namespace automation {
@@ skipping 85 matching lines @@
     heading,
     iframe,
     iframePresentational,
     ignored,
     imageMapLink,
     imageMap,
     image,
     inlineTextBox,
     labelText,
     legend,
+    lineBreak,
     link,
     listBoxOption,
     listBox,
     listItem,
     listMarker,
     list,
     locationBar,
     log,
     main,
     marquee,
@@ skipping 366 matching lines @@
     // tree with a placeholder root node; listen for the "loadComplete" event to
     // get a notification that the tree has fully loaded (the previous root node
     // reference will stop working at or before this point).
     [nocompile] static void getTree(optional long tabId, RootCallback callback);
 
     // Get the automation tree for the whole desktop which consists of all on
     // screen views. Note this API is currently only supported on Chrome OS.
     [nocompile] static void getDesktop(RootCallback callback);
   };
 };