Remove sleep.h dependency for tests

test/CMakeLists.txt

 # Enable the tests
 
-# Allow the test files to find headers in src/ since we rely on
-# SleepForMilliseconds(int milliseconds) in options_test.cc
-include_directories(${PROJECT_SOURCE_DIR}/src)
-
 find_package(Threads REQUIRED)
 
 set(CXX03_FLAGS "${CMAKE_CXX_FLAGS}")

test/options_test.cc

 #include "benchmark/benchmark_api.h"
-#include "sleep.h"
+
+#include <chrono>
+#include <thread>
 
 void BM_basic(benchmark::State& state) {
   while (state.KeepRunning()) {
@@ -7,8 +9,14 @@ void BM_basic(benchmark::State& state) {
 }
 
 void BM_basic_slow(benchmark::State& state) {
+
+  int milliseconds = state.range_x();
+  std::chrono::duration<double, std::milli> sleep_duration {
+    static_cast<double>(milliseconds)
+  };
+
   while (state.KeepRunning()) {
-    benchmark::SleepForMilliseconds(state.range_x());
+    std::this_thread::sleep_for(sleep_duration);
   }
 }