Added memory usage function to base.

webrtc/base/memory_usage.h

+/*
+ *  Copyright (c) 2017 The WebRTC 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 in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#ifndef WEBRTC_BASE_MEMORY_USAGE_H_
+#define WEBRTC_BASE_MEMORY_USAGE_H_
+
+#include <stdint.h>
+
+namespace rtc {
+
+// Returns current memory used by the process in bytes (working set size on
+// Windows and resident set size on other platforms).
+// Returns -1 on failure.
+int64_t GetProcessResidentSizeBytes();
+
+}  // namespace rtc
+
+#endif  // WEBRTC_BASE_MEMORY_USAGE_H_