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>
diff --git a/tests/PathOpsThreadedCommon.h b/tests/PathOpsThreadedCommon.h
index 1462aa2..706da6b 100644
--- a/tests/PathOpsThreadedCommon.h
+++ b/tests/PathOpsThreadedCommon.h
@@ -11,9 +11,10 @@
 #include "SkGraphics.h"
 #include "SkPath.h"
 #include "SkPathOps.h"
-#include "SkString.h"
 #include "SkTDArray.h"
 
+#include <string>
+
 #define PATH_STR_SIZE 512
 
 class PathOpsThreadedRunnable;
@@ -27,7 +28,7 @@
     unsigned char fB;
     unsigned char fC;
     unsigned char fD;
-    SkString fPathStr;
+    std::string fPathStr;
     const char* fKey;
     char fSerialNo[256];
     skiatest::Reporter* fReporter;