Adding Google benchmarking library.

third_party/google_benchmark/src/sleep.h

Index: third_party/google_benchmark/src/sleep.h
diff --git a/third_party/google_benchmark/src/sleep.h b/third_party/google_benchmark/src/sleep.h
new file mode 100644
index 0000000000000000000000000000000000000000..f98551afe28491f41077dbfaa2b526231061968b
--- /dev/null
+++ b/third_party/google_benchmark/src/sleep.h
@@ -0,0 +1,15 @@
+#ifndef BENCHMARK_SLEEP_H_
+#define BENCHMARK_SLEEP_H_
+
+namespace benchmark {
+const int kNumMillisPerSecond = 1000;
+const int kNumMicrosPerMilli = 1000;
+const int kNumMicrosPerSecond = kNumMillisPerSecond * 1000;
+const int kNumNanosPerMicro = 1000;
+const int kNumNanosPerSecond = kNumNanosPerMicro * kNumMicrosPerSecond;
+
+void SleepForMilliseconds(int milliseconds);
+void SleepForSeconds(double seconds);
+}  // end namespace benchmark
+
+#endif  // BENCHMARK_SLEEP_H_