Add picture pile raster times histogram

cc/tile_manager.cc

Index: cc/tile_manager.cc
diff --git a/cc/tile_manager.cc b/cc/tile_manager.cc
index 9935de5d2e84e1a130b685ac8ef0864213a46ae0..83c0ab2b235d2f557631804d14967b174ae1e1bb 100644
--- a/cc/tile_manager.cc
+++ b/cc/tile_manager.cc
@@ -10,6 +10,7 @@
 #include "base/debug/trace_event.h"
 #include "base/json/json_writer.h"
 #include "base/logging.h"
+#include "base/metrics/histogram.h"
 #include "cc/platform_color.h"
 #include "cc/raster_worker_pool.h"
 #include "cc/resource_pool.h"
@@ -762,7 +763,23 @@ void TileManager::RunRasterTask(uint8* buffer,
   bitmap.setPixels(buffer);
   SkDevice device(bitmap);
   SkCanvas canvas(&device);
+
+  base::TimeTicks begin_time;
+  if (stats)
+    begin_time = base::TimeTicks::Now();
+
   picture_pile->Raster(&canvas, rect, contents_scale, stats);
+
+  if (stats) {
+    base::TimeTicks end_time = base::TimeTicks::Now();
+    base::TimeDelta duration = end_time - begin_time;

[danakj, 2013/02/04 18:56:24]

nit: i think i'd drop the "duration" variable, I dont think it's adding much
here, and just put end_time-begin_time on the line below.

+    stats->totalRasterizeTime += duration;
+    UMA_HISTOGRAM_CUSTOM_COUNTS(
+      "Renderer4.PictureRasterTimeMS",
+      duration.InMilliseconds(),
+      0, 10, 10
+    );
+  }
 }
 
 // static