Uses SNPRINT macro where possible. Otherwise uses #define for format.

runtime/vm/disassembler_x64.cc

Index: runtime/vm/disassembler_x64.cc
diff --git a/runtime/vm/disassembler_x64.cc b/runtime/vm/disassembler_x64.cc
index 9f43a387ba81ce8d31f8280e3867d6eeec7713f4..d08eb16482930f2d0f5a053ee270326dc70d98cf 100644
--- a/runtime/vm/disassembler_x64.cc
+++ b/runtime/vm/disassembler_x64.cc
@@ -796,10 +796,9 @@ static const char* ObjectToCStringNoGC(const Object& obj) {
 
   const Class& clazz = Class::Handle(obj.clazz());
   const char* full_class_name = clazz.ToCString();
-  const char* format = "instance of %s";
-  intptr_t len = OS::SNPrint(NULL, 0, format, full_class_name) + 1;
-  char* chars = Thread::Current()->zone()->Alloc<char>(len);
-  OS::SNPrint(chars, len, format, full_class_name);
+  char* chars = NULL;
+  SNPRINT(chars, Thread::Current()->zone()->Alloc<char>, "instance of %s",
+          full_class_name);
   return chars;
 }