[scheduler] Add RendererScheduler.TaskDurationPerQueueType.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 9dab252cb5b8ab5b8fb5b5d8f885396e16afd2c8..895c12dd3df291b896cee32a231a07e93cc49b7f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -56047,6 +56047,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="RendererScheduler.TaskDurationPerQueueType"
+    enum="RendererSchedulerTaskQueueType" units="ms">
+  <owner>altimin@chromium.org,alexclarke@chromium.org</owner>
+  <summary>
+    Total duration of renderer tasks split per task queue type. Used to monitor
+    usage of each type of task queues. Reported each time when task is completed
+    and current accumulated duration is longer than 1ms.

[Ilya Sherman, 2017/03/16 21:23:43]

Please document that this histogram is not intended to be analyzed using the
dashboard, but rather with manual scripts, because the dashboards cannot help to
identify problematic outliers for this histogram structure.

[altimin, 2017/03/16 23:44:23]

Done.

+  </summary>
+</histogram>
+
 <histogram name="RendererScheduler.TaskQueueManager.DelayedTaskLateness"
     units="ms">
   <owner>alexclarke@chromium.org</owner>