Long press menu (shift+f6) to toggle spoken feedback.

chrome/browser/ui/ash/chrome_shell_delegate_chromeos.cc

 // Copyright 2013 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/ui/ash/chrome_shell_delegate.h"
 
+#include "ash/accelerators/spoken_feedback_toggler.h"
 #include "ash/accessibility_delegate.h"
 #include "ash/magnifier/magnifier_key_scroller.h"
 #include "ash/media_delegate.h"
 #include "ash/wm/mru_window_tracker.h"
 #include "ash/wm/window_util.h"
 #include "base/command_line.h"
 #include "base/prefs/pref_service.h"
 #include "chrome/browser/accessibility/accessibility_events.h"
 #include "chrome/browser/app_mode/app_mode_utils.h"
 #include "chrome/browser/chrome_notification_types.h"
@@ skipping 31 matching lines @@
   // because some windows can be opened in background while login UI
   // is still active because we currently restore browser windows
   // before login UI is deleted.
   ash::Shell* shell = ash::Shell::GetInstance();
   ash::MruWindowTracker::WindowList mru_list =
       shell->mru_window_tracker()->BuildMruWindowList();
   if (!mru_list.empty())
     mru_list.front()->Focus();
 
   // Enable magnifier accelerators as there may be no mouse cursor in
   // kiosk mode.

[xiyuan, 2014/02/14 01:50:21]

Update the comment?

[oshima, 2014/02/14 18:03:25]

Done.

   ash::MagnifierKeyScroller::SetEnabled(chrome::IsRunningInForcedAppMode());
+  ash::SpokenFeedbackToggler::SetEnabled(chrome::IsRunningInForcedAppMode());
 }
 
 class AccessibilityDelegateImpl : public ash::AccessibilityDelegate {
  public:
   AccessibilityDelegateImpl() {}
   virtual ~AccessibilityDelegateImpl() {}
 
   virtual void ToggleHighContrast() OVERRIDE {
     DCHECK(chromeos::AccessibilityManager::Get());
     chromeos::AccessibilityManager::Get()->EnableHighContrast(
@@ skipping 223 matching lines @@
   registrar_.Add(this,
                  chrome::NOTIFICATION_LOGIN_USER_PROFILE_PREPARED,
                  content::NotificationService::AllSources());
   registrar_.Add(this,
                  chrome::NOTIFICATION_SESSION_STARTED,
                  content::NotificationService::AllSources());
   registrar_.Add(this,
                  chrome::NOTIFICATION_APP_TERMINATING,
                  content::NotificationService::AllSources());
 }