Add histograms to track the number of job controller and job that are

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 a9161fccf87273ba6849d47cc82dfe9844199e0b..aaf5ef3cdc8e5627ef8caea52cc979c01d706087 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -33959,6 +33959,33 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Net.JobControllerSet.CountOfNonPreconnectAltJob"
+    units="alt_jobs">
+  <owner>zhongyi@chromium.org</owner>
+  <summary>
+    This counts number of alternative jobs which are still alive when
+    HttpStreamFactory is destructed.
+  </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 when HttpStreamFactory
+    is destructed.
+  </summary>
+</histogram>
+
+<histogram name="Net.JobControllerSet.CountOfPreconnect"
+    units="job_controllers">
+  <owner>zhongyi@chromium.org</owner>
+  <summary>
+    This counts number of job controllers which are used for preconnect and are
+    still alive when HttpStreamFactory is destructed.
+  </summary>
+</histogram>
+
 <histogram name="Net.LoadPrefetch.Pattern" enum="PrefetchStatus">
   <owner>droger@chromium.org</owner>
   <owner>mattcary@chromium.org</owner>