Reland [Tracing] V8 Tracing Controller

src/libplatform/tracing/trace-writer.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 SRC_LIBPLATFORM_TRACING_TRACE_WRITER_H_
+#define SRC_LIBPLATFORM_TRACING_TRACE_WRITER_H_
+
+#include "include/libplatform/v8-tracing.h"
+
+namespace v8 {
+namespace platform {
+namespace tracing {
+
+class JSONTraceWriter : public TraceWriter {
+ public:
+  explicit JSONTraceWriter(std::ostream& stream);
+  ~JSONTraceWriter();
+  void AppendTraceEvent(TraceObject* trace_event) override;
+  void Flush() override;
+
+ private:
+  std::ostream& stream_;
+  bool append_comma_ = false;
+};
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8
+
+#endif  // SRC_LIBPLATFORM_TRACING_TRACE_WRITER_H_