Better document and image viewing experience in Gmail and Google Drive
Google has launched a new version of the UI for viewing documents and images in Gmail and Google Drive to give more focus to the content itself. The tool bar has moved to the top (and disappears when not in use) and the document/image frame is now wider, giving users a more streamlined experience.
Release track:
Rapid release, with Scheduled release coming in two weeks (for Gmail only, changes in Drive will launch to all tracks today)
Reference by : http://www.google.com