Use scoped_nsobject to ensure our intermediate objects get cleaned up.

atom/browser/mac/atom_application.h

@@ -3,12 +3,13 @@
 // found in the LICENSE file.
 
 #import "base/mac/scoped_sending_event.h"
+#import "base/mac/scoped_nsobject.h"
 
 @interface AtomApplication : NSApplication<CrAppProtocol,
                                            CrAppControlProtocol> {
  @private
   BOOL handlingSendEvent_;
-  NSUserActivity* currentActivity_;
+  base::scoped_nsobject<NSUserActivity> currentActivity_;
 }
 
 + (AtomApplication*)sharedApplication;