Identity Resizer not documented

[SchusterEmilia]

Prerequisites

Please answer the following question for yourself before submitting an issue.

• I checked to make sure that this issue has not been filed already.

1. The entire URL of the documentation with the issue

https://github.com/tensorflow/models/blob/master/research/object_detection/protos/image_resizer.proto

2. Describe the issue

The IdentityResizer option is missing documentation as to what it does. I.e. how it resizes the images. The commit that added this option is also missing any mention of this image resizer.