message: Mentions key if tf.Feature parsing fails due to unsupported value.
diff: @@ -448,8 +448,8 @@ class _ParseOpParams(object):
  for key in sorted(features.keys()):
  feature = features[key]
  if not isinstance(feature, tuple(types)):
  - raise ValueError("Unsupported %s %s." %
  - (type(feature).__name__, feature))
  + raise ValueError("Unsupported %s %s for key '%s')." %
  + (type(feature).__name__, feature, key))
  params._add_feature(key, feature) # pylint: disable=protected-access
  params._validate() # pylint: disable=protected-access
  return params
  