Add platform ifdefs, fix up some MSVC warnings
diff --git a/src/core/transport/stream_op.c b/src/core/transport/stream_op.c
index c77c8cd..555543f 100644
--- a/src/core/transport/stream_op.c
+++ b/src/core/transport/stream_op.c
@@ -63,7 +63,7 @@
 }
 
 void grpc_stream_ops_unref_owned_objects(grpc_stream_op *ops, size_t nops) {
-  int i;
+  size_t i;
   for (i = 0; i < nops; i++) {
     switch (ops[i].type) {
       case GRPC_OP_SLICE: