Hardcode the UseCounter enum values so that we don't get off-by-one errors when an enum value is deleted.

After this patch, we can also get rid of all the REMOVED* enum values.

Review URL: https://codereview.chromium.org/159263003

git-svn-id: svn://svn.chromium.org/blink/trunk@166884 bbb929c8-8fbe-4397-9dbb-9b2b20218538