[tracing] Add support for TracedValue JSON serializer.

src/tracing/traced-value.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_TRACED_VALUE_H_
+#define V8_TRACING_TRACED_VALUE_H_
+
+#include <stddef.h>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "include/v8-platform.h"
+#include "src/base/macros.h"
+
+namespace v8 {
+namespace tracing {
+
+class TracedValue : public ConvertableToTraceFormat {
+ public:
+  ~TracedValue() override;
+
+  static std::unique_ptr<TracedValue> Create();
+
+  void EndDictionary();
+  void EndArray();
+
+  // These methods assume that |name| is a long lived "quoted" string.
+  void SetInteger(const char* name, int value);
+  void SetDouble(const char* name, double value);
+  void SetBoolean(const char* name, bool value);
+  void SetString(const char* name, const std::string& value);
+  void BeginDictionary(const char* name);
+  void BeginArray(const char* name);
+
+  void AppendInteger(int);
+  void AppendDouble(double);
+  void AppendBoolean(bool);
+  void AppendString(const std::string&);
+  void BeginArray();
+  void BeginDictionary();
+
+  // ConvertableToTraceFormat implementation.
+  void AppendAsTraceFormat(std::string* out) const override;
+
+ private:
+  TracedValue();
+
+  void WriteComma();
+  void WriteName(const char* name);
+
+#ifdef DEBUG
+  // In debug builds checks the pairings of {Begin,End}{Dictionary,Array}
+  std::vector<bool> nesting_stack_;
+#endif
+
+  std::string data_;
+  bool first_item_;
+
+  DISALLOW_COPY_AND_ASSIGN(TracedValue);
+};
+
+}  // namespace tracing
+}  // namespace v8
+
+#endif  // V8_TRACING_TRACED_VALUE_H_