[Tracing] Implement TracingCategoryObserver.

include/v8-tracing.h

Index: include/v8-tracing.h
diff --git a/include/v8-tracing.h b/include/v8-tracing.h
new file mode 100644
index 0000000000000000000000000000000000000000..dfa144e2dd788b4409703c7cd3baedce7d5b00e2
--- /dev/null
+++ b/include/v8-tracing.h
@@ -0,0 +1,29 @@
+// 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_V8_TRACING_H_
+#define V8_V8_TRACING_H_
+
+#include "v8.h"  // NOLINT(build/include)
+
+namespace v8 {
+namespace tracing {
+
+class V8_EXPORT TracingCategoryObserver {
+ public:
+  enum Mode {
+    ENABLED_BY_NATIVE = 1 << 0,
+    ENABLED_BY_TRACING = 1 << 1,
+  };
+  static std::unique_ptr<TracingCategoryObserver> Create();
+  virtual ~TracingCategoryObserver() = default;
+
+ protected:
+  TracingCategoryObserver() = default;
+};
+
+}  // namespace tracing
+}  // namespace v8
+
+#endif  // V8_V8_TRACING_H_