Add a UMA histogram for measuring DetachableResourceHandler duration

content/browser/loader/detachable_resource_handler.cc

Index: content/browser/loader/detachable_resource_handler.cc
diff --git a/content/browser/loader/detachable_resource_handler.cc b/content/browser/loader/detachable_resource_handler.cc
index aa1f7bd608369121b38a115e85e91d442973b088..63e22d584afb6753747d8736992bb2e26c15e9fd 100644
--- a/content/browser/loader/detachable_resource_handler.cc
+++ b/content/browser/loader/detachable_resource_handler.cc
@@ -8,6 +8,7 @@
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/time/time.h"
 #include "content/browser/loader/null_resource_controller.h"
 #include "content/browser/loader/resource_controller.h"
@@ -240,6 +241,10 @@ void DetachableResourceHandler::OnReadCompleted(
 void DetachableResourceHandler::OnResponseCompleted(
     const net::URLRequestStatus& status,
     std::unique_ptr<ResourceController> controller) {
+  UMA_HISTOGRAM_MEDIUM_TIMES(
+      "Net.DetachableResourceHandler.Duration",
+      base::TimeTicks::Now() - request()->creation_time());
+
   // No DCHECK(!is_deferred_) as the request may have been cancelled while
   // deferred.