simplify size check in string

b/72956754

Bug: skia:
Change-Id: I50627d9c7fe84630c496f8829608cde875512da0
Reviewed-on: https://skia-review.googlesource.com/107304
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Herb Derby <herb@google.com>
3 files changed