Refine bench_record and bench_playback:

bench/BenchTimer.cpp

Index: bench/BenchTimer.cpp
diff --git a/bench/BenchTimer.cpp b/bench/BenchTimer.cpp
index 3617f9de58b243253499f65df6bf340153a6d8da..f3e8e3b0ec69483f3d298bf3772eb668cd421988 100644
--- a/bench/BenchTimer.cpp
+++ b/bench/BenchTimer.cpp
@@ -76,3 +76,19 @@ void BenchTimer::truncatedEnd() {
     fTruncatedCpu = fTruncatedSysTimer->endCpu() * fDurationScale;
     fTruncatedWall = fTruncatedSysTimer->endWall() * fDurationScale;
 }
+
+WallTimer::WallTimer() : fWall(-1.0), fSysTimer(new BenchSysTimer) {}
+
+WallTimer::~WallTimer() {
+    delete fSysTimer;
+}
+
+void WallTimer::start(double durationScale) {
+    fDurationScale = durationScale;
+    fSysTimer->startWall();
+}
+
+void WallTimer::end() {
+    fWall = fSysTimer->endWall() * fDurationScale;
+}
+