Update from https://crrev.com/316786

base/trace_event/process_memory_dump.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/trace_event/process_memory_dump.h"
+
+#include "base/json/json_writer.h"
+#include "base/values.h"
+
+namespace base {
+namespace trace_event {
+
+ProcessMemoryDump::ProcessMemoryDump() {
+}
+
+ProcessMemoryDump::~ProcessMemoryDump() {
+}
+
+void ProcessMemoryDump::AppendAsTraceFormat(std::string* out) const {
+  // Build up the [dumper name] -> [serialized snapshot] JSON dictionary.
+  DictionaryValue dict;
+  std::string json_dict;
+  // TODO(primiano): this will append here the actual dumps from the dumpers.
+  base::JSONWriter::Write(&dict, &json_dict);
+  *out += json_dict;
+}
+
+}  // namespace trace_event
+}  // namespace base