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 dea89618d11fe555de65c76fbc4f511b19b4dcb5..87612f56e473220b52d24fcfc8e8926286db5faf 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -81165,6 +81165,18 @@ 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 at most once per kWorkerThreadLoadTrackerReportingInterval
+    sec per worker thread amortized. E.g. if a worker ran a single task for X
+    seconds and then went to idle for Y seconds before it shuts down, and
+    assuming the interval rate was 1 sec, we get X samples for 100% and Y
+    samples for 0%.
+  </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>