Add GrDebugMarkerOp

Change-Id: I948838dea13d2f36194ca1043ab37e72759794e0
Reviewed-on: https://skia-review.googlesource.com/31740
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
14 files changed