[Tracing] Make TracingCategoryObserver v8 internal.

src/tracing/tracing-category-observer.h

 // Copyright 2016 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_TRACING_TRACING_CATEGORY_OBSERVER_H_
 #define V8_TRACING_TRACING_CATEGORY_OBSERVER_H_
 
 #include "include/v8-platform.h"
-#include "include/v8-tracing.h"
+#include "src/base/lazy-instance.h"
 
 namespace v8 {
 namespace tracing {
 
-class TracingCategoryObserverImpl : public TracingCategoryObserver,
-                                    public Platform::TraceStateObserver {
+class TracingCategoryObserver : public Platform::TraceStateObserver {
  public:
-  TracingCategoryObserverImpl();
-  ~TracingCategoryObserverImpl();
+  enum Mode {
+    ENABLED_BY_NATIVE = 1 << 0,
+    ENABLED_BY_TRACING = 1 << 1,
+  };
+
+  static void SetUp();
+  static void TearDown();
 
   // v8::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_