Use LapTimer in rasterize_and_record micro benchmark.

cc/debug/rasterize_and_record_benchmark.cc

Index: cc/debug/rasterize_and_record_benchmark.cc
diff --git a/cc/debug/rasterize_and_record_benchmark.cc b/cc/debug/rasterize_and_record_benchmark.cc
index b330e429d35021bf477670e96e19ac18429ac83a..acf59a70fef5f17615d5161cbf235b220bfe1292 100644
--- a/cc/debug/rasterize_and_record_benchmark.cc
+++ b/cc/debug/rasterize_and_record_benchmark.cc
@@ -11,6 +11,7 @@
 #include "base/basictypes.h"
 #include "base/strings/stringprintf.h"
 #include "base/values.h"
+#include "cc/debug/lap_timer.h"
 #include "cc/debug/rasterize_and_record_benchmark_impl.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/picture_layer.h"
@@ -24,15 +25,14 @@ namespace {
 
 const int kDefaultRecordRepeatCount = 100;
 
+// Parameters for LapTimer.
+const int kTimeLimitMillis = 1;
+const int kWarmupRuns = 0;
+const int kTimeCheckInterval = 1;
+
 const char* kModeSuffixes[Picture::RECORDING_MODE_COUNT] = {
     "", "_sk_null_canvas", "_painting_disabled", "_skrecord"};
 
-base::TimeTicks Now() {
-  return base::TimeTicks::IsThreadNowSupported()
-             ? base::TimeTicks::ThreadNow()
-             : base::TimeTicks::HighResNow();
-}
-
 }  // namespace
 
 RasterizeAndRecordBenchmark::RasterizeAndRecordBenchmark(
@@ -121,12 +121,20 @@ void RasterizeAndRecordBenchmark::RunOnLayer(PictureLayer* layer) {
     Picture::RecordingMode mode =
         static_cast<Picture::RecordingMode>(mode_index);
     base::TimeDelta min_time = base::TimeDelta::Max();
+    LapTimer timer(kWarmupRuns,

[danakj, 2014/05/12 17:16:41]

Can you move the LapTimer constant declarations down here? 

+                   base::TimeDelta::FromMilliseconds(kTimeLimitMillis),

[danakj, 2014/05/12 17:16:41]

And this could go inside the for loop?

+                   kTimeCheckInterval);
     for (int i = 0; i < record_repeat_count_; ++i) {
-      base::TimeTicks start = Now();
-      scoped_refptr<Picture> picture = Picture::Create(
-          visible_content_rect, painter, tile_grid_info, false, 0, mode);
-      base::TimeTicks end = Now();
-      base::TimeDelta duration = end - start;
+      // Run for a minimum amount of time to avoid problems with timer
+      // quantization when the layer is very small.
+      timer.Reset();
+      do {
+        scoped_refptr<Picture> picture = Picture::Create(
+            visible_content_rect, painter, tile_grid_info, false, 0, mode);
+        timer.NextLap();
+      } while (!timer.HasTimeLimitExpired());
+      base::TimeDelta duration =
+          base::TimeDelta::FromMillisecondsD(timer.MsPerLap());
       if (duration < min_time)
         min_time = duration;
     }