Rename batch->op in GrAuditTrail.

Change-Id: I68670e5ceb06716e9928ee58485d63e157c7aca7
Reviewed-on: https://skia-review.googlesource.com/6345
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
5 files changed