Fix tessellation benchmarks to not allocate new data every iteration

Change-Id: I86bb6f2690ad349e640ea997e0b71387613ebffb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/289460
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
3 files changed