Dropout Regularization.

def dropout(attrs, inputs, proto_obj):
    """Dropout Regularization."""
    mode = 'training'
    if 'is_test' in attrs and attrs['is_test'] == 0:
        mode = 'always'
    new_attrs = translation_utils._fix_attribute_names(attrs,
                                                       {'ratio': 'p'})
    new_attrs = translation_utils._remove_attributes(new_attrs, ['is_test'])
    new_attrs = translation_utils._add_extra_attributes(new_attrs, {'mode': mode})
    return 'Dropout', new_attrs, inputs