Add samplingTime mode to nanobench

tools/timer/SysTimer_mach.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SysTimer_mach.h"
 
 static time_value_t mac_cpu_time() {
     mach_port_t task = mach_task_self();
@@ skipping 21 matching lines @@
     if ((end_clock.microseconds - start_clock.microseconds) < 0) {
         duration_clock = (end_clock.seconds - start_clock.seconds-1) * 1000;
         duration_clock += (1000000 + end_clock.microseconds - start_clock.microseconds) / 1000.0;
     } else {
         duration_clock = (end_clock.seconds - start_clock.seconds) * 1000;
         duration_clock += (end_clock.microseconds - start_clock.microseconds) / 1000.0;
     }
     return duration_clock;
 }
 
+static double wall_interval_in_ms(uint64_t elapsed) {
+    mach_timebase_info_data_t sTimebaseInfo;
+    if (KERN_SUCCESS != mach_timebase_info(&sTimebaseInfo)) {
+        return 0;
+    } else {
+        uint64_t elapsedNano = elapsed * sTimebaseInfo.numer / sTimebaseInfo.denom;
+        return elapsedNano / 1000000.0;
+    }
+}
+
 void SysTimer::startWall() {
     fStartWall = mach_absolute_time();
 }
 
 void SysTimer::startCpu() {
     fStartCpu = mac_cpu_time();
 }
 
 double SysTimer::endCpu() {
     time_value_t end_cpu = mac_cpu_time();
     return interval_in_ms(fStartCpu, end_cpu);
 }
 
 double SysTimer::endWall() {
     uint64_t end_wall = mach_absolute_time();
+    return wall_interval_in_ms(end_wall - fStartWall);
+}
 
-    uint64_t elapsed = end_wall - fStartWall;
-    mach_timebase_info_data_t sTimebaseInfo;
-    if (KERN_SUCCESS != mach_timebase_info(&sTimebaseInfo)) {
-        return 0;
-    } else {
-        uint64_t elapsedNano = elapsed * sTimebaseInfo.numer / sTimebaseInfo.denom;
-        return elapsedNano / 1000000.0;
-    }
+double GetTimeMs() {
+    static const uint64_t launchTime = mach_absolute_time();
+    return wall_interval_in_ms(mach_absolute_time() - launchTime);
 }