webreview-client is the client library for the webreview (https://github.com/grow/webreview) web application. It's designed to be used by programs that need to communicate with a webreview server.
The webreview client is a simple API client, but it's primarily used to do the heavy-lifting involved with generating signed URLs for filesets and managing a fileset upload.
Once a fileset has been uploaded, the client finishes with a finalize command that indicates to the webreview server that the upload is finishde and post- upload tasks can be kicked off (such as notifications or builds).