NULL -> nullptr under athena/

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 670385f0a061fb4be2d510eb637fb33221b0c4ee..2c1ae165e779bcb4e3b7beb111429512c3548069 100644
--- a/athena/test/base/activity_lifetime_tracker.h
+++ b/athena/test/base/activity_lifetime_tracker.h
@@ -32,10 +32,10 @@ class ActivityLifetimeTracker : public ActivityManagerObserver {
   void* GetDeletedActivityAndReset();
 
  private:
-  // The activity which got created if not NULL.
+  // The activity which got created if not nullptr.
   Activity* new_activity_;
 
-  // An old activity which got unloaded if not NULL.
+  // An old activity which got unloaded if not nullptr.
   void* deleted_activity_;
 
   DISALLOW_COPY_AND_ASSIGN(ActivityLifetimeTracker);