ChangeScreen2: Show on which categories a reviewer can vote Old change screen had grey styled cells in approval table for labels a reviewer hadn't right to vote on. The new change screen uses chips to present the reviewers name and therefore this valuable information is lost. Add it back in form of tooltip with the list of votable labels for each reviewer. Bug: issue 2078 Change-Id: I0f101e43c625bfe1f181b46574c6677d930a5c19