[runtime] Minimize runtime call stats overhead when it is disabled.

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index 52688ec3fd3a4c2e30b7496d5a50e6e26c7b0f07..ed07d5d089101311f1f90c61b396e6ba61de64ca 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -147,8 +147,7 @@ BUILTIN_LIST_C(DEF_ARG_TYPE)
   V8_NOINLINE static Object* Builtin_Impl_Stats_##name(                        \
       int args_length, Object** args_object, Isolate* isolate) {               \
     name##ArgumentsType args(args_length, args_object);                        \
-    RuntimeCallStats* stats = isolate->counters()->runtime_call_stats();       \
-    RuntimeCallTimerScope timer(isolate, &stats->Builtin_##name);              \
+    RuntimeCallTimerScope timer(isolate, &RuntimeCallStats::Builtin_##name);   \
     TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.runtime"),                      \
                  "V8.Builtin_" #name);                                         \
     return Builtin_Impl_##name(args, isolate);                                 \