Keep track of accessibility focus across windows.

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 598 matching lines @@
     // tab if no tabID is given, enabling automation if necessary. Returns a
     // 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);
 
+    // Get the automation node that currently has focus, globally. Will return
+    // null if the none of the nodes in any loaded trees have focus.

[David Tseng, 2016/01/28 02:00:56]

nit: if none of

[dmazzoni, 2016/01/30 00:02:41]

Done.

+    [nocompile] static AutomationNode getFocus();
+
     // Add a tree change observer. Tree change observers are static/global, they
     // listen to changes across all trees. Pass a filter to determine what
     // specific tree changes to listen to, and note that listnening to all
     // tree changes can be expensive.
     [nocompile] static void addTreeChangeObserver(
         TreeChangeObserverFilter filter, TreeChangeObserver observer);
 
     // Remove a tree change observer.
     [nocompile] static void removeTreeChangeObserver(
         TreeChangeObserver observer);
 
     // Sets the selection in a tree. This creates a selection in a single
     // tree (anchorObject and focusObject must have the same root).
     // Everything in the tree between the two node/offset pairs gets included
     // in the selection. The anchor is where the user started the selection,
     // while the focus is the point at which the selection gets extended
     // e.g. when dragging with a mouse or using the keyboard. For nodes with
     // the role staticText, the offset gives the character offset within
     // the value where the selection starts or ends, respectively.
     [nocompile] static void setDocumentSelection(
         SetDocumentSelectionParams params);
   };
 };