Revert "Don't keep "outResultsFile" open in nanobench"

This reverts commit 2e1381ec86bc794968fca51572dd7bd37d6508c7.

Reason for revert: This causes corrupted JSON output from
                   nanobench

Bug: skia:12078

Original change's description:
> Don't keep "outResultsFile" open in nanobench
>
> There is a bug on Pixel and Pixel2 devices where the program
> eventually terminates with a non-zero exit code. Closing the
> outResultsFile between JSON flushes seems to fix it (for whatever
> reason).
>
> Bug: b/143074513
> Change-Id: I935e982e88758fda19292129c8031f8501cca615
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249821
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Chris Dalton <csmartdalton@google.com>

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: b/143074513
Change-Id: Iad8e4423acbc520f49365859020776110087dacc
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/419842
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Herb Derby <herb@google.com>
4 files changed