[tracing] Add a dump provider to dump process memory totals.

base/trace_event/process_memory_totals.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_totals.h"
+
+#include "base/trace_event/trace_event_argument.h"
+
+namespace base {
+namespace trace_event {
+
+void ProcessMemoryTotals::AsValueInto(TracedValue* value) const {
+  value->SetDouble("resident_set_bytes", resident_set_bytes_);
+}
+
+}  // namespace trace_event
+}  // namespace base