Modifies the state of the checkbox and makes an API call when a file is expanded inline. As part of this change, the logic for determining whether or not a reviewed checkbox should be checked is refactored from a computed function to a computed property set on the file itself. Also fixes a style error in the diff-builder. Bug: Issue 5798 Change-Id: Ib1297d6c6d7e000e67465c20f21913063d360ff1