arc: Provide UMA for OptIn flow.

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 cfd26dbd189b0b9e2f651959e8d4a5f10b559f5c..a9bf4f5e188b6e5bc026b322d814e1f020a89011 100644
--- a/chrome/browser/chromeos/arc/arc_session_manager.h
+++ b/chrome/browser/chromeos/arc/arc_session_manager.h
@@ -233,6 +233,9 @@ class ArcSessionManager : public ArcSessionRunner::Observer,
   void StartArcForTesting() { StartArc(); }
 
  private:
+  // Reports statuses of OptIn flow to UMA.
+  class ScopedOptInFlowTracker;
+
   // RequestEnable() has a check in order not to trigger starting procedure
   // twice. This method can be called to bypass that check when restarting.
   void RequestEnableImpl();
@@ -326,6 +329,8 @@ class ArcSessionManager : public ArcSessionRunner::Observer,
   std::unique_ptr<ArcAuthContext> context_;
   std::unique_ptr<ArcAndroidManagementChecker> android_management_checker_;
 
+  std::unique_ptr<ScopedOptInFlowTracker> scoped_opt_in_tracker_;
+
   // The time when the sign in process started.
   base::Time sign_in_start_time_;
   // The time when ARC was about to start.