Set keys to traverse accessibility tree. Using focus ring to highlight selected node.

chrome/browser/chromeos/accessibility/switch_access_event_handler.h

+// Copyright 2017 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.
+
+#ifndef CHROME_BROWSER_CHROMEOS_ACCESSIBILITY_SWITCH_ACCESS_EVENT_HANDLER_H_
+#define CHROME_BROWSER_CHROMEOS_ACCESSIBILITY_SWITCH_ACCESS_EVENT_HANDLER_H_
+
+#include "base/macros.h"
+#include "ui/events/event_handler.h"
+
+namespace chromeos {
+
+// When Switch Access is enabled, intercepts a few keys before the rest of the
+// OS has a chance to handle them, as a method for controlling the entire OS
+// with a small number of switches. The key events do not propagate to the rest
+// of the system.
+//
+// This class just intercepts the keys and forwards them to the component
+// extension.
+class SwitchAccessEventHandler : public ui::EventHandler {
+ public:
+  SwitchAccessEventHandler();
+  ~SwitchAccessEventHandler() override;
+
+ private:
+  // EventHandler:
+  void OnKeyEvent(ui::KeyEvent* event) override;
+
+  void CancelEvent(ui::Event* event);
+  void DispatchKeyEventToSwitchAccess(const ui::KeyEvent& event);
+
+  DISALLOW_COPY_AND_ASSIGN(SwitchAccessEventHandler);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_ACCESSIBILITY_SWITCH_ACCESS_EVENT_HANDLER_H_