message: IS_IN_GRAPH_MODE should not force-init the eager context.
  This caused hard to diagnose failures in enable_eager_execution calls.
diff: @@ -923,6 +923,10 @@ def add_function(fdef):
  # but they do all import this file. Note that IS_IN_GRAPH_MODE and
  # in_graph_mode are both parameterless functions.
  def _tmp_in_graph_mode():
  + if context_safe() is None:
  + # Context not yet initialized. Assume graph mode following the
  + # default implementation in `is_in_graph_mode`.
  + return True
  return not executing_eagerly()
  