code: private static Frame toFrame(Matrix m, Key<Frame> key) {
      H2O.submitTask(new ConvertMatrixToFrame(m, key)).join();
      Frame f = DKV.getGet(key);
      assert f != null;
      return f;
    }
docs: Helper to convert a Matrix into a Frame
  
  @param m Matrix
  @param key Key for output Frame
  @return Reference to Frame (which is also in DKV)