[Tracing] Use TracingCategoryObserver in runtime statistics

src/counters.cc

 // 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.
 
 #include "src/counters.h"
 
 #include <iomanip>
 
 #include "src/base/platform/platform.h"
 #include "src/isolate.h"
@@ skipping 326 matching lines @@
 #undef PRINT_COUNTER
 
 #define PRINT_COUNTER(name) entries.Add(&this->Handler_##name);
   FOR_EACH_HANDLER_COUNTER(PRINT_COUNTER)
 #undef PRINT_COUNTER
 
   entries.Print(os);
 }
 
 void RuntimeCallStats::Reset() {
-  if (!FLAG_runtime_call_stats &&
-      !TRACE_EVENT_RUNTIME_CALL_STATS_TRACING_ENABLED())
+  if (V8_LIKELY(FLAG_runtime_stats == 0)) {

[alph, 2016/10/31 20:46:53]

nit: no need {} for return;

[lpy, 2016/10/31 20:54:19]

I think Yang once mentioned V8 prefers {}

[alph, 2016/10/31 21:17:19]

Interesting. the code style guide
https://google.github.io/styleguide/cppguide.html states that you don't need {}
for single-line statements

     return;
+  }
 #define RESET_COUNTER(name) this->name.Reset();
   FOR_EACH_MANUAL_COUNTER(RESET_COUNTER)
 #undef RESET_COUNTER
 
 #define RESET_COUNTER(name, nargs, result_size) this->Runtime_##name.Reset();
   FOR_EACH_INTRINSIC(RESET_COUNTER)
 #undef RESET_COUNTER
 
 #define RESET_COUNTER(name) this->Builtin_##name.Reset();
   BUILTIN_LIST_C(RESET_COUNTER)
@@ skipping 37 matching lines @@
 #define DUMP_COUNTER(name) \
   if (this->Handler_##name.count > 0) this->Handler_##name.Dump(value);
   FOR_EACH_HANDLER_COUNTER(DUMP_COUNTER)
 #undef DUMP_COUNTER
 
   in_use_ = false;
 }
 
 }  // namespace internal
 }  // namespace v8