Delete long-expired GlobalSdch field trial.

chrome/renderer/page_load_histograms.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/renderer/page_load_histograms.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 398 matching lines @@
                   begin_to_finish_doc);
     PLT_HISTOGRAM("PLT.BeginToFinish_ContentPrefetcherReferrer",
                   begin_to_finish_all_loads);
   }
 
   // Histograms to determine if SDCH has an impact.
   // TODO(jar): Consider removing per-link load types and the enumeration.
   static const bool use_sdch_histogram =
       base::FieldTrialList::TrialExists("GlobalSdch");
   if (use_sdch_histogram) {
-    UMA_HISTOGRAM_ENUMERATION(
-        base::FieldTrial::MakeName("PLT.LoadType", "GlobalSdch"),
-        load_type, DocumentState::kLoadTypeMax);
+    UMA_HISTOGRAM_ENUMERATION("PLT.LoadType", load_type,
+                              DocumentState::kLoadTypeMax);
     switch (load_type) {
       case DocumentState::NORMAL_LOAD:
-        PLT_HISTOGRAM(base::FieldTrial::MakeName(
-            "PLT.BeginToFinish_NormalLoad", "GlobalSdch"),
-            begin_to_finish_all_loads);
+        PLT_HISTOGRAM("PLT.BeginToFinish_NormalLoad",

[jar (doing other things), 2013/05/28 18:35:02]

You'll notice that this exact histogram is already gathered on line 364.

This whole section, starting at line 418, and ending at line 445, is *only* done
*IF* we have a field trial.  IF we don't have a field trial, then we don't do
the MakeName combination.

Bottom line: You should remove all code from line 414 to line 445 when you rip
out the field trial.

The pattern seen here is VERY common, and consists of:

a) Check to see if there is a histogram of the given name.
b) If there is one, then record some special variants on *existing* histograms,
using the MakeName() helper.

[Alexei Svitkine (slow), 2013/05/28 18:48:58]

Ah, you're absolutely right! Done.

+                      begin_to_finish_all_loads);
         break;
       case DocumentState::LINK_LOAD_NORMAL:
-        PLT_HISTOGRAM(base::FieldTrial::MakeName(
-            "PLT.BeginToFinish_LinkLoadNormal", "GlobalSdch"),
-            begin_to_finish_all_loads);
+        PLT_HISTOGRAM("PLT.BeginToFinish_LinkLoadNormal",
+                      begin_to_finish_all_loads);
         break;
       case DocumentState::LINK_LOAD_RELOAD:
-        PLT_HISTOGRAM(base::FieldTrial::MakeName(
-            "PLT.BeginToFinish_LinkLoadReload", "GlobalSdch"),
-            begin_to_finish_all_loads);
+        PLT_HISTOGRAM("PLT.BeginToFinish_LinkLoadReload",
+                      begin_to_finish_all_loads);
         break;
       case DocumentState::LINK_LOAD_CACHE_STALE_OK:
-        PLT_HISTOGRAM(base::FieldTrial::MakeName(
-            "PLT.BeginToFinish_LinkLoadStaleOk", "GlobalSdch"),
-            begin_to_finish_all_loads);
+        PLT_HISTOGRAM("PLT.BeginToFinish_LinkLoadStaleOk",
+                      begin_to_finish_all_loads);
         break;
       case DocumentState::LINK_LOAD_CACHE_ONLY:
-        PLT_HISTOGRAM(base::FieldTrial::MakeName(
-            "PLT.BeginToFinish_LinkLoadCacheOnly", "GlobalSdch"),
-            begin_to_finish_all_loads);
+        PLT_HISTOGRAM("PLT.BeginToFinish_LinkLoadCacheOnly",
+                      begin_to_finish_all_loads);
         break;
       default:
         break;
     }
   }
 
   // TODO(mpcomplete): remove the extension-related histograms after we collect
   // enough data. http://crbug.com/100411
   const bool use_adblock_histogram =
       chrome::ChromeContentRendererClient::IsAdblockInstalled();
@@ skipping 292 matching lines @@
 
   DCHECK(document_state);
   DCHECK(ds);
   GURL url(ds->request().url());
   Time start = document_state->start_load_time();
   Time finish = document_state->finish_load_time();
   // TODO(mbelshe): should we log more stats?
   VLOG(1) << "PLT: " << (finish - start).InMilliseconds() << "ms "
           << url.spec();
 }