fix pathops_unittest test strings

Using std::string is tons faster than SkString;
multiple callers to std::string don't run into
thread contention but SkString does.

R=csmartdalton@google.com

Change-Id: I0357c6a9c73856bfffbb76e65c275acdfe7d8159
Reviewed-on: https://skia-review.googlesource.com/13471
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Cary Clark <caryclark@google.com>
2 files changed