athena: Expose the list of activities from the ActivityManager.

athena/test/base/activity_lifetime_tracker.h

Index: athena/test/base/activity_lifetime_tracker.h
diff --git a/athena/test/base/activity_lifetime_tracker.h b/athena/test/base/activity_lifetime_tracker.h
index 0e6c23312df043a03f847a63bbaf443fd4c6c336..d217893ce7be9623c756583e9813ba64f60c1a0a 100644
--- a/athena/test/base/activity_lifetime_tracker.h
+++ b/athena/test/base/activity_lifetime_tracker.h
@@ -17,11 +17,10 @@ class ActivityLifetimeTracker : public ActivityManagerObserver {
   ActivityLifetimeTracker();
   ~ActivityLifetimeTracker() override;
 
-  // Called after an |activity| got created.
+  // ActivityManagerObserver:
   void OnActivityStarted(Activity* activity) override;
-
-  // Called before an |activity| gets destroyed.
   void OnActivityEnding(Activity* activity) override;
+  void OnActivityOrderChanged() override;
 
   // Returns the newly created activity (if any) and resets its reference.
   Activity* GetNewActivityAndReset();