Added GetCpuTime to base/ to get total CPU time consumed by process for perf tests.

webrtc/base/cpu_time.cc

+/*
+ *  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.
+ */
+
+#include "webrtc/base/cpu_time.h"
+#include "webrtc/base/logging.h"
+
+#if defined(WEBRTC_LINUX)
+#include <time.h>
+#elif defined(WEBRTC_MAC)
+#include <unistd.h>
+#include <sys/resource.h>
+#include <sys/times.h>
+#elif defined(WEBRTC_WIN)
+#include <windows.h>
+#endif
+
+namespace rtc {
+
+//  static
+double CpuTime::GetCpuTime() {
+#if defined(WEBRTC_LINUX)
+  struct timespec ts;
+  if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts) != -1) {
+    return static_cast<double>(ts.tv_sec) +
+           static_cast<double>(ts.tv_nsec) / 1000000000.0;

[nisse-webrtc, 2017/02/15 12:18:16]

I'd prefer "* 1e-9", so I don't have to count the zeros. And 1e-6 below. (There
are also integer constants, like rtc::kNumNanosecontsPerSecond).

[ilnik, 2017/02/15 12:53:21]

Done.

+  } else {
+    LOG(LS_ERROR) << "clock_gettime() failed.";
+  }
+#elif defined(WEBRTC_MAC)
+  struct rusage rusage;
+  if (getrusage(RUSAGE_SELF, &rusage) != -1) {
+    return static_cast<double>(rusage.ru_utime.tv_sec) +
+           static_cast<double>(rusage.ru_utime.tv_usec) / 1000000.0;
+  }
+#elif defined(WEBRTC_WIN)
+  FILETIME createTime;
+  FILETIME exitTime;
+  FILETIME kernelTime;
+  FILETIME userTime;
+  if (GetProcessTimes(GetCurrentProcess(), &createTime, &exitTime, &kernelTime,
+                      &userTime) != -1) {
+    SYSTEMTIME userSystemTime;

[nisse-webrtc, 2017/02/15 12:18:16]

After a quick look at the windows docs, I'd recommend accessing the FILETIME
fields directly.

  (static_cast<uint64_t>(userTime.dwHighDateTime) << 32)
    + userTime.dwLowDateTime.

or something like that. Converting to hours and seconds is a waste of cycles.
And note that left shift of signed values is undefined behavior in C (not sure
about C++), hence the use of an unsigned type.

[ilnik, 2017/02/15 12:53:21]

Done.

+    if (FileTimeToSystemTime(&userTime, &userSystemTime) != -1)
+      return static_cast<double>(userSystemTime.wHour) * 3600.0 +
+             static_cast<double>(userSystemTime.wMinute) * 60.0 +
+             static_cast<double>(userSystemTime.wSecond) +
+             static_cast<double>(userSystemTime.wMilliseconds) / 1000.0;
+  } else {
+    LOG(LS_ERROR) << "GetProcessTimes() failed.";
+  }
+#else
+  LOG(LS_ERROR) << "No function to get CPU time";
+#endif
+  return -1.0;
+}
+
+}  // namespace rtc