Remove a UMA histogram for measuring DetachableResourceHandler duration

Bug: 709910,759934
Change-Id: I265d4c376a9fb68e577c1b1412564a614b48fc91
Reviewed-on: https://chromium-review.googlesource.com/757988Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Takeshi Yoshino <tyoshino@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515930}

content/browser/loader/detachable_resource_handler.cc

@@ -8,7 +8,6 @@
 
 #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"
@@ -236,10 +235,6 @@ 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.
 

tools/metrics/histograms/histograms.xml

@@ -41125,6 +41125,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="Net.DetachableResourceHandler.Duration" units="ms">
+  <obsolete>
+    Removed in Chrome 64.
+  </obsolete>
   <owner>yhirano@chromium.org</owner>
   <summary>
     Duration of time that a request associated with DetachableResourceHandler