message: Give a reference of the Checkpoint to the Status objects returned by restore. The _graph_view field only holds a weakref. Without this fix, if the Checkpoint object is released, the Status' methods become unusable.
diff: @@ -685,6 +685,8 @@ class CheckpointLoadStatus(_LoadStatus):
  self._checkpoint = checkpoint
  self._feed_dict = feed_dict
  self._graph_view = graph_view
  + # Keep a reference to the root, since graph_view might only have a weakref.
  + self._root = graph_view.root
  def assert_consumed(self):
  """Asserts that all objects in the checkpoint have been created/matched.
  @@ -845,6 +847,8 @@ class InitializationOnlyStatus(_LoadStatus):
  def __init__(self, graph_view, restore_uid):
  self._restore_uid = restore_uid
  self._graph_view = graph_view
  + # Keep a reference to the root, since graph_view might only have a weakref.
  + self._root = graph_view.root
  def assert_consumed(self):
  """Assertion for consistency with `CheckpointLoadStatus`. Always fails."""
  @@ -920,6 +924,9 @@ class NameBasedSaverStatus(_LoadStatus):
  def __init__(self, checkpoint, graph_view):
  self._checkpoint = checkpoint
  self._graph_view = graph_view
  + # Keep a reference to the root, since graph_view might only have a weakref.
  + self._root = graph_view.root
  +
  def assert_consumed(self):
  """Raises an exception if any variables/objects are unmatched."""
  