Fix leaks in skdiff

The skdiff code leaks some file names. Instead of augmenting the
existing manual ownership, give everything an owner.

Change-Id: I8bc2cb39ad4176bb3be645710ae28271f5b12ff9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437000
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
3 files changed