Indicate either in the Review Materials overview, or in the file differences view when a file has been moved or renamed.
This information is tracked by a number of Version Control systems, and clearly indicated when examining the differences between commits/check-ins. Currently a moved or renamed file will show up as completely removed from the old location (all contents removed) and completely added to the new location (all contents added). If changes were also made within the file in the same range of commits/check-ins under review, they can't be differentiated.
As a possible implementation, both the old and new file names in the Review Materials overview could link to the same file differences view where the before and after file names are listed as different at the top of the window (where there's currently only one center-aligned file name as of 11.0.11000).
