Warmup for one extra frame in nanobench

On ANGLE, at least, this frame gives us much more consistent results.

Bug: skia:
Change-Id: Ifdecc8451ef51490c08057645214738180b1a366
Reviewed-on: https://skia-review.googlesource.com/57884
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed