Remove explicit singletonness of ArcBridgeService part 4.

chrome/browser/chromeos/arc/arc_session_manager.h

Index: chrome/browser/chromeos/arc/arc_session_manager.h
diff --git a/chrome/browser/chromeos/arc/arc_session_manager.h b/chrome/browser/chromeos/arc/arc_session_manager.h
index 8c1469759e7f71a4f35edc00c9c9fb1cfdbec9f3..91ca023cf6b60f58ff238a486faaccf1ea3fa048 100644
--- a/chrome/browser/chromeos/arc/arc_session_manager.h
+++ b/chrome/browser/chromeos/arc/arc_session_manager.h
@@ -201,6 +201,8 @@ class ArcSessionManager : public ArcService,
 
   void OnProvisioningFinished(ProvisioningResult result);
 
+  void SetAttemptUserExitCallbackForTesting(const base::Closure& callback);
+
  private:
   // Negotiates the terms of service to user.
   void StartTermsOfServiceNegotiation();
@@ -248,6 +250,7 @@ class ArcSessionManager : public ArcService,
   std::unique_ptr<ArcAndroidManagementChecker> android_management_checker_;
 
   base::Time sign_in_time_;
+  base::Closure attempt_user_exit_callback_;
 
   base::WeakPtrFactory<ArcSessionManager> weak_ptr_factory_;