code: public static int w(String tag, Throwable tr) {
          collectLogEntry(Constants.WARN, tag, "", null);
          if (isLoggable(tag, Constants.WARN)) {
              return android.util.Log.w(tag, tr);
          }
          return 0;
      }
docs: Send a {@link #Constants.WARN} log message and log the exception.
  
  @param tr
  An exception to log