message: Implement resources for feature_columns_v2.
diff: @@ -274,6 +274,10 @@ class _StateManagerImpl(StateManager):
  self._trainable = trainable
  self._layer = layer
  self._cols_to_vars_map = collections.defaultdict(lambda: {})
  + # TODO(vbardiovsky): Make sure the resources are tracked by moving them to
  + # the layer (inheriting from AutoTrackable), e.g.:
  + # self._layer._resources_map = data_structures.Mapping()
  + self._cols_to_resources_map = collections.defaultdict(lambda: {})
  def create_variable(self,
  feature_column,
  @@ -305,6 +309,14 @@ class _StateManagerImpl(StateManager):
  return self._cols_to_vars_map[feature_column][name]
  raise ValueError('Variable does not exist.')
  + def add_resource(self, feature_column, name, resource):
  + self._cols_to_resources_map[feature_column][name] = resource
  +
  + def get_resource(self, feature_column, name):
  + if name in self._cols_to_resources_map[feature_column]:
  + return self._cols_to_resources_map[feature_column][name]
  + raise ValueError('Resource does not exist.')
  +
  class _BaseFeaturesLayer(Layer):
  """Base class for DenseFeatures and SequenceFeatures.
  