Drafts are saved as inline comments for images when user comments mock

Summary: Drafts are saved as inline comments for images when user comments mock.

Test Plan: Verified that drafts receive transactionphid when user comments mock.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2446

Differential Revision: https://secure.phabricator.com/D4850