cros: Only preload the lock screen; do not reuse it.

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

Index: chrome/browser/chromeos/login/session/chrome_session_manager.h
diff --git a/chrome/browser/chromeos/login/session/chrome_session_manager.h b/chrome/browser/chromeos/login/session/chrome_session_manager.h
index a9978125dd12c37dbc62a09e44ce2b97825340fe..7c5129234e9279c869eb5a2301479335a38fedc0 100644
--- a/chrome/browser/chromeos/login/session/chrome_session_manager.h
+++ b/chrome/browser/chromeos/login/session/chrome_session_manager.h
@@ -16,8 +16,6 @@ class Profile;
 
 namespace chromeos {
 
-class IdleDetector;
-
 class ChromeSessionManager : public session_manager::SessionManager {
  public:
   ChromeSessionManager();
@@ -40,9 +38,6 @@ class ChromeSessionManager : public session_manager::SessionManager {
                           bool browser_restart) override;
 
  private:
-  // Used to preload the lock screen when the user is inactive.
-  std::unique_ptr<IdleDetector> idle_detector_;
-
   DISALLOW_COPY_AND_ASSIGN(ChromeSessionManager);
 };