code: public int getActivityIndex(ResolveInfo activity) {
          List<ActivityResolveInfo> activities = mActivites;
          final int activityCount = activities.size();
          for (int i = 0; i < activityCount; i++) {
              ActivityResolveInfo currentActivity = activities.get(i);
              if (currentActivity.resolveInfo == activity) {
                  return i;
              }
          }
          return INVALID_INDEX;
      }
docs: Gets the index of a the given activity.
  
  @param activity The activity index.
  
  @return The index if found, -1 otherwise.