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

webrtc/base/cpu_time_unittest.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/platform_thread.h"
+#include "webrtc/base/timeutils.h"
+#include "webrtc/test/gtest.h"
+
+namespace internal {
+const double kAllowedErrorSec = 0.1;
+const int kProcessingTimeSec = 1;
+
+bool WaitingFunction(void* counter_pointer) {
+  int64_t &counter = *reinterpret_cast<int64_t*>(counter_pointer);
+  counter = 0;
+  int64_t stop_time =
+      rtc::SystemTimeNanos() + kProcessingTimeSec * rtc::kNumNanosecsPerSec;
+  while (rtc::SystemTimeNanos() < stop_time) {
+    counter++;
+  }
+  return true;
+}
+}  // namespace internal
+
+namespace rtc {
+
+TEST(GetCpuTimeTest, SingleThread) {
+  double start = CpuTime::GetCpuTime();
+  int64_t *counter = new int64_t;
+  ::internal::WaitingFunction(reinterpret_cast<void*>(counter));
+  EXPECT_GT(*counter, 0);
+  delete counter;
+  double duration = CpuTime::GetCpuTime() - start;
+  EXPECT_GE(duration,
+            ::internal::kProcessingTimeSec - ::internal::kAllowedErrorSec);
+  EXPECT_LE(duration,
+            ::internal::kProcessingTimeSec + ::internal::kAllowedErrorSec);
+}
+
+TEST(GetCpuTimeTest, TwoThreads) {
+  double start = CpuTime::GetCpuTime();
+  int64_t* counter1 = new int64_t;
+  int64_t* counter2 = new int64_t;
+  PlatformThread thread1(::internal::WaitingFunction,
+                         reinterpret_cast<void*>(counter1), "Thread1");
+  PlatformThread thread2(::internal::WaitingFunction,
+                         reinterpret_cast<void*>(counter2), "Thread2");
+  thread1.Start();
+  thread2.Start();
+  thread1.Stop();
+  thread2.Stop();
+
+  EXPECT_GE(*counter1, 0);
+  EXPECT_GE(*counter2, 0);
+  delete counter1;
+  delete counter2;
+  double duration = CpuTime::GetCpuTime() - start;
+  EXPECT_GE(duration,
+            2 * ::internal::kProcessingTimeSec - ::internal::kAllowedErrorSec);
+  //  If .Stop() also consumes CPU time, there will be 3 active threads.
+  EXPECT_LE(duration,
+            3 * ::internal::kProcessingTimeSec + ::internal::kAllowedErrorSec);
+}
+
+}  // namespace rtc