add bench for textblobbuilder

Bug: skia:
Change-Id: I133c6f78f1b378c3a86dd91b59990861b5e0d09a
Reviewed-on: https://skia-review.googlesource.com/c/174840
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed