cros: Preload and reuse the lock screen across lock sessions

chrome/browser/chromeos/login/session/chrome_session_manager.cc

Index: chrome/browser/chromeos/login/session/chrome_session_manager.cc
diff --git a/chrome/browser/chromeos/login/session/chrome_session_manager.cc b/chrome/browser/chromeos/login/session/chrome_session_manager.cc
index 194efe6379c98e87ab6343df008c229fc507cdcb..e6030f8413b88d1bea9eae4fbe143f52d7d6c897 100644
--- a/chrome/browser/chromeos/login/session/chrome_session_manager.cc
+++ b/chrome/browser/chromeos/login/session/chrome_session_manager.cc
@@ -17,6 +17,8 @@
 #include "chrome/browser/chromeos/app_mode/kiosk_app_manager.h"
 #include "chrome/browser/chromeos/arc/arc_service_launcher.h"
 #include "chrome/browser/chromeos/boot_times_recorder.h"
+#include "chrome/browser/chromeos/idle_detector.h"
+#include "chrome/browser/chromeos/login/lock/webui_screen_locker.h"
 #include "chrome/browser/chromeos/login/login_wizard.h"
 #include "chrome/browser/chromeos/login/session/user_session_manager.h"
 #include "chrome/browser/chromeos/login/wizard_controller.h"
@@ -44,6 +46,9 @@ namespace chromeos {
 
 namespace {
 
+// Duration of user inactivity before preloading the lock screen.
+constexpr int kIdleSecondsBeforePreloadingLockScreen = 8;
+
 // Whether kiosk auto launch should be started.
 bool ShouldAutoLaunchKioskApp(const base::CommandLine& command_line) {
   KioskAppManager* app_manager = KioskAppManager::Get();
@@ -232,6 +237,13 @@ void ChromeSessionManager::SessionStarted() {
       content::Source<session_manager::SessionManager>(this),
       content::Details<const user_manager::User>(
           user_manager->GetActiveUser()));
+
+  if (chromeos::WebUIScreenLocker::ShouldShareLockScreen()) {
+    idle_detector_ = base::MakeUnique<chromeos::IdleDetector>(
+        base::Bind(&chromeos::WebUIScreenLocker::Preload));
+    idle_detector_->Start(
+        base::TimeDelta::FromSeconds(kIdleSecondsBeforePreloadingLockScreen));
+  }
 }
 
 void ChromeSessionManager::NotifyUserLoggedIn(const AccountId& user_account_id,