Split JobController count histograms into three separate histograms:

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 52f9a6bfe21b4cb28d55fca4f5483e2b27f2ead8..7ed4fe44778593a01874a17281d76520799e9be2 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -34968,44 +34968,57 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="Net.JobControllerSet.CountOfJobControllerAtShutDown"
+<histogram
+    name="Net.JobControllerSet.CountOfJobController.NonPreconnect.PendingRequest"
     units="job_controllers">
   <owner>zhongyi@chromium.org</owner>
   <summary>
-    This counts number of all the job controllers that are still alive.
+    This counts number of JobControllers that are still alive, not created for
+    preconnect, and still have a HttpStreamFactoryImpl::Request pending.
   </summary>
 </histogram>
 
-<histogram name="Net.JobControllerSet.CountOfNonPreconnectAltJob"
-    units="alt_jobs">
+<histogram
+    name="Net.JobControllerSet.CountOfJobController.NonPreconnect.RequestGone"
+    units="job_controllers">
   <owner>zhongyi@chromium.org</owner>
   <summary>
-    This counts number of alternative jobs which are still alive.
+    This counts number of job controllers that are still alive, not created for
+    preconnect but HttpStreamFactoryImpl::Request has completed.
   </summary>
 </histogram>
 
-<histogram name="Net.JobControllerSet.CountOfNonPreconnectMainJob"
-    units="main_jobs">
+<histogram name="Net.JobControllerSet.CountOfJobController.Preconnect"
+    units="job_controllers">
   <owner>zhongyi@chromium.org</owner>
-  <summary>This counts number of main jobs which are still alive.</summary>
+  <summary>
+    This counts number of job controllers which are used for preconnect and are
+    still alive.
+  </summary>
 </histogram>
 
-<histogram name="Net.JobControllerSet.CountOfPendingRequest" units="requests">

[xunjieli, 2017/04/19 15:12:14]

I think the recommended way is to deprecate the old histogram and not remove it.

+<histogram name="Net.JobControllerSet.CountOfJobControllerAtShutDown"
+    units="job_controllers">
   <owner>zhongyi@chromium.org</owner>
   <summary>
-    This counts number of HttpStreamFactoryImpl::Request which are still alive.
+    This counts number of all the job controllers that are still alive.
   </summary>
 </histogram>
 
-<histogram name="Net.JobControllerSet.CountOfPreconnect"
-    units="job_controllers">
+<histogram name="Net.JobControllerSet.CountOfNonPreconnectAltJob"
+    units="alt_jobs">
   <owner>zhongyi@chromium.org</owner>
   <summary>
-    This counts number of job controllers which are used for preconnect and are
-    still alive.
+    This counts number of alternative jobs which are still alive.
   </summary>
 </histogram>
 
+<histogram name="Net.JobControllerSet.CountOfNonPreconnectMainJob"
+    units="main_jobs">
+  <owner>zhongyi@chromium.org</owner>
+  <summary>This counts number of main jobs which are still alive.</summary>
+</histogram>
+
 <histogram name="Net.LoadPrefetch.Pattern" enum="PrefetchStatus">
   <owner>droger@chromium.org</owner>
   <owner>mattcary@chromium.org</owner>