Fix build with SK_SUPPORT_UNITTEST on

src/animator/SkScriptTokenizer.cpp

Index: src/animator/SkScriptTokenizer.cpp
diff --git a/src/animator/SkScriptTokenizer.cpp b/src/animator/SkScriptTokenizer.cpp
index f789d388a79a046f2abad5ad9c6d3415fda62a72..42954a7706089e77c86b0d00662725cb4684c21c 100644
--- a/src/animator/SkScriptTokenizer.cpp
+++ b/src/animator/SkScriptTokenizer.cpp
@@ -1479,7 +1479,7 @@ static const SkScriptNAnswer2 scriptTests[]  = {
 void SkScriptEngine2::UnitTest() {
 #if defined(SK_SUPPORT_UNITTEST)
     ValidateDecompileTable();
-    for (int index = 0; index < SkScriptNAnswer_testCount; index++) {
+    for (size_t index = 0; index < SkScriptNAnswer_testCount; index++) {
         SkScriptEngine2 engine(scriptTests[index].fType);
         SkScriptValue2 value;
         const char* script = scriptTests[index].fScript;