[counters] Put all counter work behind flags

src/arguments.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ARGUMENTS_H_
 #define V8_ARGUMENTS_H_
 
 #include "src/allocation.h"
 #include "src/isolate.h"
 #include "src/tracing/trace-event.h"
@@ skipping 258 matching lines @@
 #ifdef DEBUG
 #define CLOBBER_DOUBLE_REGISTERS() ClobberDoubleRegisters(1, 2, 3, 4);
 #else
 #define CLOBBER_DOUBLE_REGISTERS()
 #endif
 
 #define RUNTIME_FUNCTION_RETURNS_TYPE(Type, Name)                          \
   static INLINE(Type __RT_impl_##Name(Arguments args, Isolate* isolate));  \
   Type Name(int args_length, Object** args_object, Isolate* isolate) {     \
     CLOBBER_DOUBLE_REGISTERS();                                            \
-    Arguments args(args_length, args_object);                              \
     Type value;                                                            \
     TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.runtime"), "V8." #Name);    \
+    Arguments args(args_length, args_object);                              \

[Camillo Bruni, 2016/03/10 12:45:47]

apparently this has some positive effects when microbenchmarking
SunSpiderGolemStringFasta.js

     if (FLAG_runtime_call_stats) {                                         \
       RuntimeCallStats* stats = isolate->counters()->runtime_call_stats(); \
       RuntimeCallTimerScope timer(isolate, &stats->Name);                  \
       value = __RT_impl_##Name(args, isolate);                             \
     } else {                                                               \
       value = __RT_impl_##Name(args, isolate);                             \
     }                                                                      \
     return value;                                                          \
   }                                                                        \
   static Type __RT_impl_##Name(Arguments args, Isolate* isolate)
 
 #define RUNTIME_FUNCTION(Name) RUNTIME_FUNCTION_RETURNS_TYPE(Object*, Name)
 #define RUNTIME_FUNCTION_RETURN_PAIR(Name) \
     RUNTIME_FUNCTION_RETURNS_TYPE(ObjectPair, Name)
 #define RUNTIME_FUNCTION_RETURN_TRIPLE(Name) \
     RUNTIME_FUNCTION_RETURNS_TYPE(ObjectTriple, Name)
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ARGUMENTS_H_