Split JobController count histograms into three separate histograms:

net/http/http_stream_factory_impl.cc

Index: net/http/http_stream_factory_impl.cc
diff --git a/net/http/http_stream_factory_impl.cc b/net/http/http_stream_factory_impl.cc
index a16c22f9edb8cf4f1dee822791727ba60ece2169..532611dc08a96aca8bbf066c3261e23247d8bc35 100644
--- a/net/http/http_stream_factory_impl.cc
+++ b/net/http/http_stream_factory_impl.cc
@@ -372,8 +372,8 @@ void HttpStreamFactoryImpl::AddJobControllerCountToHistograms() {
 
   int alt_job_count = 0;
   int main_job_count = 0;
-  int pending_request_count = 0;
-  int preconnect_controller_count = 0;
+  size_t pending_request_count = 0;

[xunjieli, 2017/04/19 15:12:13]

nit: s/pending_request_count/num_controllers_with_request

[Zhongyi Shi, 2017/04/19 17:38:53]

Done.

+  size_t preconnect_controller_count = 0;

[xunjieli, 2017/04/19 15:12:13]

nit: s/preconnect_controller_count/num_controllers_for_preconnect

[Zhongyi Shi, 2017/04/19 17:38:53]

Done.

   for (const auto& job_controller : job_controller_set_) {
     DCHECK(job_controller->HasPendingAltJob() ||
            job_controller->HasPendingMainJob());
@@ -394,14 +394,24 @@ void HttpStreamFactoryImpl::AddJobControllerCountToHistograms() {
     if (job_controller->HasPendingMainJob())
       main_job_count++;
   }
-  UMA_HISTOGRAM_COUNTS_1M("Net.JobControllerSet.CountOfPreconnect",
-                          preconnect_controller_count);
+  UMA_HISTOGRAM_COUNTS_1M(
+      "Net.JobControllerSet.CountOfJobController.Preconnect",
+      preconnect_controller_count);
+  UMA_HISTOGRAM_COUNTS_1M(
+      "Net.JobControllerSet.CountOfJobCOntroller.NonPerconnect.PendingRequest",

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

s/COntroller/Controller
s/Perconnect/Preconnect

[Zhongyi Shi, 2017/04/19 17:38:53]

Done.

+      pending_request_count);
+
+  DCHECK_GE(job_controller_set_.size() - preconnect_controller_count,
+            pending_request_count);

[xunjieli, 2017/04/19 15:12:13]

nit: can we calculate this value and DCHECK on it?
DCHECK_GE(num_controllers_with_no_request, 0);

UMA_HISTOGRAM...(... num_controllers_with_no_request);

[Zhongyi Shi, 2017/04/19 17:38:53]

DCHECK_GE(job_controller_set_.size() - preconnect_controller_count,          
pending_request_count) does the DCHECK and prevents overflow. 

[xunjieli, 2017/04/19 17:50:04]

We can't depend on DCHECK doing the overflow check since we won't have it in
release build.

I think it's fine to assume there is no overflow because in one iteration, we
either increment num_controllers_with_request or num_controllers_for_preconnect
and not both.

So |job_controller_set_.size()| should be greater or equal to sum of
num_controllers_with_request and num_controller_for_preconnect.

I think we should get rid of the DCHECK. 

+  UMA_HISTOGRAM_COUNTS_1M(
+      "Net.JobControllerSet.CountOfJobController.NonPreconnect.RequestGone",
+      job_controller_set_.size() - preconnect_controller_count -
+          pending_request_count);
+
   UMA_HISTOGRAM_COUNTS_1M("Net.JobControllerSet.CountOfNonPreconnectAltJob",
                           alt_job_count);
   UMA_HISTOGRAM_COUNTS_1M("Net.JobControllerSet.CountOfNonPreconnectMainJob",
                           main_job_count);
-  UMA_HISTOGRAM_COUNTS_1M("Net.JobControllerSet.CountOfPendingRequest",
-                          pending_request_count);
 }
 
 void HttpStreamFactoryImpl::DumpMemoryStats(