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

chrome/browser/chromeos/accessibility/switch_access_event_handler.cc

+// 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.
+
+#include "chrome/browser/chromeos/accessibility/switch_access_event_handler.h"
+
+#include "ash/shell.h"
+#include "base/logging.h"
+#include "chrome/browser/chromeos/accessibility/accessibility_manager.h"
+#include "chrome/browser/chromeos/accessibility/event_handler_common.h"
+#include "chrome/common/extensions/extension_constants.h"
+#include "extensions/browser/extension_host.h"
+#include "ui/events/event.h"
+
+namespace chromeos {
+
+SwitchAccessEventHandler::SwitchAccessEventHandler() {
+  if (ash::Shell::HasInstance())
+    ash::Shell::GetInstance()->AddPreTargetHandler(this);
+}
+
+SwitchAccessEventHandler::~SwitchAccessEventHandler() {
+  if (ash::Shell::HasInstance())
+    ash::Shell::GetInstance()->RemovePreTargetHandler(this);
+}
+
+void SwitchAccessEventHandler::OnKeyEvent(ui::KeyEvent* event) {
+  DCHECK(event);
+
+  ui::KeyboardCode key_code = event->key_code();
+  if (key_code == ui::VKEY_1 || key_code == ui::VKEY_2 ||
+      key_code == ui::VKEY_3 || key_code == ui::VKEY_4 ||
+      key_code == ui::VKEY_5) {
+    CancelEvent(event);
+    LOG(ERROR) << "Dispatching key " << key_code - ui::VKEY_0
+               << " to switch access";
+    DispatchKeyEventToSwitchAccess(*event);
+  }
+}
+
+void SwitchAccessEventHandler::CancelEvent(ui::Event* event) {
+  DCHECK(event);
+  if (event->cancelable()) {
+    event->SetHandled();
+    event->StopPropagation();
+  }
+}
+
+void SwitchAccessEventHandler::DispatchKeyEventToSwitchAccess(
+    const ui::KeyEvent& event) {
+  extensions::ExtensionHost* host =
+      GetAccessibilityExtensionHost(extension_misc::kSwitchAccessExtensionId);
+  ForwardKeyToExtension(event, host);
+}
+
+}  // namespace chromeos