The chrome.screenlockPrivate API allows select apps to control the ChromeOS ScreenLocker.

chrome/browser/chromeos/extensions/screenlock_private_api.cc

+// Copyright (c) 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/chromeos/extensions/screenlock_private_api.h"
+
+#include "base/lazy_instance.h"
+#include "base/values.h"
+#include "chrome/browser/chromeos/login/screen_locker.h"
+#include "chrome/browser/extensions/event_router.h"
+#include "chrome/browser/extensions/extension_system.h"
+#include "chrome/common/extensions/api/screenlock_private.h"
+#include "chromeos/dbus/dbus_thread_manager.h"
+
+using chromeos::ScreenLocker;
+
+namespace screenlock = extensions::api::screenlock_private;
+
+namespace extensions {
+
+ScreenlockPrivateGetLockedFunction::ScreenlockPrivateGetLockedFunction() {}
+
+ScreenlockPrivateGetLockedFunction::~ScreenlockPrivateGetLockedFunction() {}
+
+bool ScreenlockPrivateGetLockedFunction::RunImpl() {
+  bool locked = false;
+  ScreenLocker* locker = ScreenLocker::default_screen_locker();
+  if (locker)
+    locked = locker->locked();
+  SetResult(new base::FundamentalValue(locked));
+  SendResponse(error_.empty());
+  return true;
+}
+
+ScreenlockPrivateSetLockedFunction::ScreenlockPrivateSetLockedFunction() {}
+
+ScreenlockPrivateSetLockedFunction::~ScreenlockPrivateSetLockedFunction() {}
+
+bool ScreenlockPrivateSetLockedFunction::RunImpl() {
+  scoped_ptr<screenlock::SetLocked::Params> params(
+      screenlock::SetLocked::Params::Create(*args_));
+  EXTENSION_FUNCTION_VALIDATE(params.get());
+  if (params->locked) {
+    ScreenLocker::Show();

[xiyuan, 2013/11/13 20:47:30]

Let's do the locking via session manager.

BusThreadManager::Get()->GetSessionManagerClient()->RequestLockScreen();

This would make sure correct upstart signal is emitted and all interested
daemons are notified.

[benjhayden, 2013/11/13 21:42:22]

Done.

+  } else {
+    ScreenLocker* locker = ScreenLocker::default_screen_locker();
+    if (locker)
+      ScreenLocker::Hide();
+  }
+  SendResponse(error_.empty());
+  return true;
+}
+
+ScreenlockPrivateShowMessageFunction::ScreenlockPrivateShowMessageFunction() {}
+
+ScreenlockPrivateShowMessageFunction::~ScreenlockPrivateShowMessageFunction() {}
+
+bool ScreenlockPrivateShowMessageFunction::RunImpl() {
+  scoped_ptr<screenlock::SetLocked::Params> params(
+      screenlock::SetLocked::Params::Create(*args_));
+  EXTENSION_FUNCTION_VALIDATE(params.get());
+  ScreenLocker* locker = ScreenLocker::default_screen_locker();
+  if (!locker) {
+    SendResponse(error_.empty());
+    return true;
+  }
+  // TODO locker->ShowMessage(params->message);
+  SendResponse(error_.empty());
+  return true;
+}
+
+ScreenlockPrivateEventRouter::ScreenlockPrivateEventRouter(Profile* profile)
+    : profile_(profile) {
+  chromeos::SessionManagerClient* session_manager =
+      chromeos::DBusThreadManager::Get()->GetSessionManagerClient();
+  if (!session_manager->HasObserver(this))
+    session_manager->AddObserver(this);
+}
+
+ScreenlockPrivateEventRouter::~ScreenlockPrivateEventRouter() {}
+
+void ScreenlockPrivateEventRouter::ScreenIsLocked() {
+  DispatchEvent(screenlock::OnChanged::kEventName,
+      new base::FundamentalValue(true));
+}
+
+void ScreenlockPrivateEventRouter::ScreenIsUnlocked() {
+  DispatchEvent(screenlock::OnChanged::kEventName,
+      new base::FundamentalValue(false));
+}
+
+void ScreenlockPrivateEventRouter::DispatchEvent(
+    const std::string& event_name,
+    base::Value* arg) {
+  scoped_ptr<base::ListValue> args(new base::ListValue());
+  args->Append(arg);
+  scoped_ptr<extensions::Event> event(new extensions::Event(
+      event_name, args.Pass()));
+  extensions::ExtensionSystem::Get(profile_)->event_router()->
+      BroadcastEvent(event.Pass());
+}
+
+static base::LazyInstance<extensions::ProfileKeyedAPIFactory<
+    ScreenlockPrivateEventRouter> >
+    g_factory = LAZY_INSTANCE_INITIALIZER;
+
+// static
+extensions::ProfileKeyedAPIFactory<ScreenlockPrivateEventRouter>*
+ScreenlockPrivateEventRouter::GetFactoryInstance() {
+  return &g_factory.Get();
+}
+
+void ScreenlockPrivateEventRouter::Shutdown() {
+  chromeos::SessionManagerClient* session_manager =
+      chromeos::DBusThreadManager::Get()->GetSessionManagerClient();
+  if (session_manager->HasObserver(this))
+    session_manager->RemoveObserver(this);
+}
+
+}  // namespace extensions