[profiler] Introduce lightweight mode for Rutime Call Stats collection.

src/tracing/tracing-category-observer.cc

Index: src/tracing/tracing-category-observer.cc
diff --git a/src/tracing/tracing-category-observer.cc b/src/tracing/tracing-category-observer.cc
index 710488a1c300e135cdef661a6ce0949bac8d4928..e6bd06ae17547fa2257152c1fb23eee2d20111c6 100644
--- a/src/tracing/tracing-category-observer.cc
+++ b/src/tracing/tracing-category-observer.cc
@@ -18,6 +18,8 @@ void TracingCategoryObserver::SetUp() {
   v8::internal::V8::GetCurrentPlatform()->AddTraceStateObserver(
       TracingCategoryObserver::instance_);
   TRACE_EVENT_WARMUP_CATEGORY(TRACE_DISABLED_BY_DEFAULT("v8.runtime_stats"));
+  TRACE_EVENT_WARMUP_CATEGORY(
+      TRACE_DISABLED_BY_DEFAULT("v8.runtime_stats_sampling"));
 }
 
 void TracingCategoryObserver::TearDown() {
@@ -33,10 +35,16 @@ void TracingCategoryObserver::OnTraceEnabled() {
   if (enabled) {
     v8::internal::FLAG_runtime_stats |= ENABLED_BY_TRACING;
   }
+  TRACE_EVENT_CATEGORY_GROUP_ENABLED(
+      TRACE_DISABLED_BY_DEFAULT("v8.runtime_stats_sampling"), &enabled);
+  if (enabled) {
+    v8::internal::FLAG_runtime_stats |= ENABLED_BY_SAMPLING;
+  }
 }
 
 void TracingCategoryObserver::OnTraceDisabled() {
-  v8::internal::FLAG_runtime_stats &= ~ENABLED_BY_TRACING;
+  v8::internal::FLAG_runtime_stats &=
+      ~(ENABLED_BY_TRACING | ENABLED_BY_SAMPLING);
 }
 
 }  // namespace tracing