Use int for size when printing to stdout.

runtime/bin/builtin_natives.cc

Index: runtime/bin/builtin_natives.cc
diff --git a/runtime/bin/builtin_natives.cc b/runtime/bin/builtin_natives.cc
index 80844970dfdce2206c604a829b1ab45166994337..47dd211cd573e5af5cc1f5032c160851027cdc23 100644
--- a/runtime/bin/builtin_natives.cc
+++ b/runtime/bin/builtin_natives.cc
@@ -111,7 +111,7 @@ void FUNCTION_NAME(Logger_PrintString)(Dart_NativeArguments args) {
     // interrupt.
     Platform::PrintBlocking(stdout, "%s\n", Dart_GetError(result));
   } else {
-    Platform::PrintBlocking(stdout, "%.*s\n", length, chars);
+    Platform::PrintBlocking(stdout, "%.*s\n", static_cast<int>(length), chars);
   }
 }