Make a pre-read A/B field-trial

chrome/browser/browser_main_win.cc

 // Copyright (c) 2011 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/browser/browser_main.h"
 #include "chrome/browser/browser_main_win.h"
 
 #include <windows.h>
 #include <shellapi.h>
 
@@ skipping 72 matching lines @@
   }
 }
 
 void RecordBrowserStartupTime() {
   // Calculate the time that has elapsed from our own process creation.
   FILETIME creation_time = {};
   FILETIME ignore = {};
   ::GetProcessTimes(::GetCurrentProcess(), &creation_time, &ignore, &ignore,
       &ignore);
 
-  base::TimeDelta elapsed_from_startup =
-      base::Time::Now() - base::Time::FromFileTime(creation_time);
-
-  // Record the time to present in a histogram.
-  UMA_HISTOGRAM_MEDIUM_TIMES("Startup.BrowserMessageLoopStartTime",
-                             elapsed_from_startup);
+  RecordPreReadExperimentTime(
+      "Startup.BrowserMessageLoopStartTime",
+      base::Time::Now() - base::Time::FromFileTime(creation_time));
 }
 
 int AskForUninstallConfirmation() {
   int ret = content::RESULT_CODE_NORMAL_EXIT;
   views::Widget::CreateWindow(new UninstallView(ret))->Show();
   views::AcceleratorHandler accelerator_handler;
   MessageLoopForUI::current()->Run(&accelerator_handler);
   return ret;
 }
 
@@ skipping 206 matching lines @@
       crypto::EnsureNSPRInit();
     }
   }
 };
 
 // static
 BrowserMainParts* BrowserMainParts::CreateBrowserMainParts(
     const MainFunctionParams& parameters) {
   return new BrowserMainPartsWin(parameters);
 }