user_manager: Remove deps on session_manager

Move session started flag and code from user_manager to
session manager and remove the deps on session_manager.

BUG=657149

Review-Url: https://codereview.chromium.org/2438063002
Cr-Commit-Position: refs/heads/master@{#427773}
diff --git a/components/user_manager/user_manager_base.h b/components/user_manager/user_manager_base.h
index 094588e..2986d2f 100644
--- a/components/user_manager/user_manager_base.h
+++ b/components/user_manager/user_manager_base.h
@@ -57,7 +57,7 @@
                     bool browser_restart) override;
   void SwitchActiveUser(const AccountId& account_id) override;
   void SwitchToLastActiveUser() override;
-  void SessionStarted() override;
+  void OnSessionStarted() override;
   void RemoveUser(const AccountId& account_id,
                   RemoveUserDelegate* delegate) override;
   void RemoveUserFromList(const AccountId& account_id) override;
@@ -97,7 +97,6 @@
   bool IsLoggedInAsKioskApp() const override;
   bool IsLoggedInAsArcKioskApp() const override;
   bool IsLoggedInAsStub() const override;
-  bool IsSessionStarted() const override;
   bool IsUserNonCryptohomeDataEphemeral(
       const AccountId& account_id) const override;
   bool IsUserCryptohomeDataEphemeral(
@@ -337,9 +336,6 @@
   // Indicates stage of loading user from prefs.
   UserLoadStage user_loading_stage_ = STAGE_NOT_LOADED;
 
-  // True if SessionStarted() has been called.
-  bool session_started_ = false;
-
   // Cached flag of whether currently logged-in user is owner or not.
   // May be accessed on different threads, requires locking.
   bool is_current_user_owner_ = false;