[tracing] Implement composable memory usage estimators.

base/test/scoped_memory_usage.h

+// Copyright 2016 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.
+
+#ifndef BASE_TEST_SCOPED_MEMORY_USAGE_H_
+#define BASE_TEST_SCOPED_MEMORY_USAGE_H_
+
+#include <stddef.h>
+
+#include "base/macros.h"
+
+namespace base {
+namespace test {
+
+class ScopedMemoryUsage {
+ public:
+  ScopedMemoryUsage();
+  ~ScopedMemoryUsage();
+
+  size_t Usage() const;
+
+  static void Initialize();
+};
+
+}  // namespace test
+}  // namespace base
+
+#endif  // BASE_TEST_SCOPED_MEMORY_USAGE_H_