Bug 876456 - (2) Raise an exception if adb getTopActivity fails; r=jmaher

testing/mozbase/mozdevice/mozdevice/droid.py

@@ -121,7 +121,7 @@ class DroidADB(DeviceManagerADB, DroidMixin):
             if m:
                 package = m.group(1)
         if not package:
-            print "Warning: getTopActivity unable to find focused app"
+            raise DMError("unable to find focused app")
         return package
 
 class DroidSUT(DeviceManagerSUT, DroidMixin):