Checking that there are no more than 2 live activities at any moment

This is tightening the makeshift strictmode criteria.

Starting with this moment, we will know that there is
no memory growth during tests execution, which is a big deal.

Big: 139137636

Change-Id: I5edc84524463bd1736d727496ad0fc031bb9624c

tests/src/com/android/launcher3/ui/ActivityLeakTracker.java

@@ -77,6 +77,8 @@ class ActivityLeakTracker implements Application.ActivityLifecycleCallbacks {
             }
         }
 
+        if (liveActivities > 2)  return false;
+
         // It's OK to have 1 leaked activity if no active activities exist.
         return liveActivities == 0 ? destroyedActivities <= 1 : destroyedActivities == 0;
     }