WorkerThread CPU Load UMA

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 eefa4a24637aad338e86374450a6d29bb7a3930e..c759ec8d7adb99eaf3ec54b362b3ace1af354259 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -80097,6 +80097,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="WorkerScheduler.WorkerThreadLoad" units="%">
+  <owner>kinuko@chromium.org</owner>
+  <summary>
+    Worker thread load, i.e. percentage of time spent on running tasks. This
+    metric is emitted when the worker thread task is completed.

[falken, 2017/03/23 06:48:05]

Should we elaborate here about the reporting interval? If I understand
correctly, if the worker ran a single task for 10 seconds, and we have a 1
second reporting interval, and the worker lived for 30 seconds, would we have 30
samples: 20 samples of 0% and 10 samples of 100%?

And if the worker ran 5 tasks, each 100ms, and we have a 1 second reporting
interval we'd see 1 sample for 50% load?

+  </summary>
+</histogram>
+
 <histogram name="WorkerThread.DebuggerTask.Time" units="ms">
   <owner>nhiroki@chromium.org</owner>
   <summary>The time taken for running a debugger task on WorkerThread.</summary>