[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 3862a2a74878c1b5548e0c7d4fd1ea39742e0ae0..6abd88010a01581fb0a2fde505a7e5decd2b88b5 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -58914,6 +58914,19 @@ 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

[Ilya Sherman, 2017/05/15 22:53:22]

nit: s/queues/queue

[altimin, 2017/05/16 11:56:14]

Done.

+    and current accumulated duration is longer than 1ms.
+
+    This metric is susceptible to problematic outliers and should be analyzed
+    with custom scripts accounting for that rather than from a dashboard.
+  </summary>
+</histogram>
+
 <histogram name="RendererScheduler.TaskQueueManager.DelayedTaskLateness"
     units="ms">
   <owner>alexclarke@chromium.org</owner>