Split setter (private method).

def _set_splits(self, split_dict):
    """Split setter (private method)."""
    # Update the dictionary representation.
    # Use from/to proto for a clean copy
    self._splits = split_dict.copy()

    # Update the proto
    del self.as_proto.splits[:]  # Clear previous
    for split_info in split_dict.to_proto():
      self.as_proto.splits.add().CopyFrom(split_info)