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

src/tracing/tracing-category-observer.h

Index: src/tracing/tracing-category-observer.h
diff --git a/src/tracing/tracing-category-observer.h b/src/tracing/tracing-category-observer.h
index 0a4e05df715296f6f17b0e7f6b7afe4a659470c0..66dd2d78f11419eb50f3a715261796f53cba3fa1 100644
--- a/src/tracing/tracing-category-observer.h
+++ b/src/tracing/tracing-category-observer.h
@@ -6,7 +6,6 @@
 #define V8_TRACING_TRACING_CATEGORY_OBSERVER_H_
 
 #include "include/v8-platform.h"
-#include "src/base/lazy-instance.h"
 
 namespace v8 {
 namespace tracing {
@@ -16,6 +15,7 @@ class TracingCategoryObserver : public Platform::TraceStateObserver {
   enum Mode {
     ENABLED_BY_NATIVE = 1 << 0,
     ENABLED_BY_TRACING = 1 << 1,
+    ENABLED_BY_SAMPLING = 1 << 2,
   };
 
   static void SetUp();
@@ -25,13 +25,11 @@ class TracingCategoryObserver : public Platform::TraceStateObserver {
   void OnTraceEnabled() final;
   void OnTraceDisabled() final;
 
-  TracingCategoryObserver() {}
-  ~TracingCategoryObserver() {}
-
  private:
   static TracingCategoryObserver* instance_;
 };
 
 }  // namespace tracing
 }  // namespace v8
+
 #endif  // V8_TRACING_TRACING_CATEGORY_OBSERVER_H_