Update `nameVariable` to return the variable name directly.

Previously, the generated name was passed back in a SkString-pointer
output parameter. Directly returning the SkString simplified nearly
every call site, and made none of them worse.

Change-Id: Ied57adcf8fb087a301641adad437d8a68f8d3297
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/329622
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
8 files changed