Add path utils, plus a test for it.

gm/gm_expectations.cpp

Index: gm/gm_expectations.cpp
diff --git a/gm/gm_expectations.cpp b/gm/gm_expectations.cpp
index 71311d5e116d6fa7c923352b9e3f3576f5fb0124..36a1d1f48e017f1983ab72e2c65d26723c6aa766 100644
--- a/gm/gm_expectations.cpp
+++ b/gm/gm_expectations.cpp
@@ -8,6 +8,7 @@
 #include "gm_expectations.h"
 #include "SkBitmapHasher.h"
 #include "SkImageDecoder.h"
+#include "SkOSPathUtils.h"
 
 #define DEBUGFAIL_SEE_STDERR SkDEBUGFAIL("see stderr for message")
 
@@ -34,15 +35,6 @@ namespace skiagm {
         va_end(args);
     }
 
-    SkString SkPathJoin(const char *rootPath, const char *relativePath) {
-        SkString result(rootPath);
-        if (!result.endsWith(SkPATH_SEPARATOR)) {
-            result.appendUnichar(SkPATH_SEPARATOR);
-        }
-        result.append(relativePath);
-        return result;
-    }
-
     // TODO(epoger): This currently assumes that the result SkHashDigest was
     // generated as an SkHashDigest of an SkBitmap.  We'll need to allow for other
     // hash types to cover non-bitmaps.