Roll back PreRead experiment

This CL removes the pre-read experiment introduced in revision 95579.
http://src.chromium.org/viewvc/chrome?view=rev&revision=95579

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/7690007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@97556 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 11 insertions, 54 deletions

diff --git a/chrome/browser/browser_main.cc b/chrome/browser/browser_main.cc
index be43c54..34a18d7 100644
--- a/chrome/browser/browser_main.cc
+++ b/chrome/browser/browser_main.cc
@@ -165,7 +165,6 @@
 #include <commctrl.h>
 #include <shellapi.h>
 
-#include "base/environment.h"  // For PreRead experiment.
 #include "base/win/scoped_com_initializer.h"
 #include "base/win/windows_version.h"
 #include "chrome/browser/browser_trial.h"
@@ -784,20 +783,6 @@ void SetSocketReusePolicy(int warmest_socket_trial_group,
   net::SetSocketReusePolicy(result - socket_policy);
 }
 
-// This code is specific to the Windows-only PreReadExperiment field-trial.
-void AddPreReadHistogramTime(const char* name, base::TimeDelta time) {
-  const base::TimeDelta kMin(base::TimeDelta::FromMilliseconds(1));
-  const base::TimeDelta kMax(base::TimeDelta::FromHours(1));
-  static const size_t kBuckets(100);
-
-  // FactoryTimeGet will always return a pointer to the same histogram object,
-  // keyed on its name. There's no need for us to store it explicitly anywhere.
-  base::Histogram* counter = base::Histogram::FactoryTimeGet(
-      name, kMin, kMax, kBuckets, base::Histogram::kUmaTargetedHistogramFlag);
-
-  counter->AddTime(time);
-}
-
 #if defined(USE_LINUX_BREAKPAD)
 bool IsCrashReportingEnabled(const PrefService* local_state) {
   // Check whether we should initialize the crash reporter. It may be disabled
@@ -2061,8 +2046,12 @@ int BrowserMain(const MainFunctionParams& parameters) {
       if (pool)
         pool->Recycle();
 
-      RecordPreReadExperimentTime("Startup.BrowserOpenTabs",
-                                  base::TimeTicks::Now() - browser_open_start);
+      UMA_HISTOGRAM_CUSTOM_TIMES(
+          "Startup.BrowserOpenTabs",
+          base::TimeTicks::Now() - browser_open_start,
+          base::TimeDelta::FromMilliseconds(1),
+          base::TimeDelta::FromHours(1),
+          100);
 
       // TODO(mad): Move this call in a proper place on CrOS.
       // http://crosbug.com/17687
@@ -2157,31 +2146,3 @@ int BrowserMain(const MainFunctionParams& parameters) {
   TRACE_EVENT_END_ETW("BrowserMain", 0, 0);
   return result_code;
 }
-
-// This code is specific to the Windows-only PreReadExperiment field-trial.
-void RecordPreReadExperimentTime(const char* name, base::TimeDelta time) {
-  DCHECK(name != NULL);
-
-  // This gets called with different histogram names, so we don't want to use
-  // the UMA_HISTOGRAM_CUSTOM_TIMES macro--it uses a static variable, and the
-  // first call wins.
-  AddPreReadHistogramTime(name, time);
-
-#if defined(OS_WIN)
-  static const char kEnvVar[] = "CHROME_PRE_READ_EXPERIMENT";
-
-  // The pre-read experiment is Windows specific.
-  scoped_ptr<base::Environment> env(base::Environment::Create());
-  DCHECK(env.get() != NULL);
-
-  // Only record the sub-histogram result if the experiment is running
-  // (environment variable is set, and valid).
-  std::string pre_read;
-  if (env->GetVar(kEnvVar, &pre_read) && (pre_read == "0" || pre_read == "1")) {
-    std::string uma_name(name);
-    uma_name += "_PreRead";
-    uma_name += pre_read == "1" ? "Enabled" : "Disabled";
-    AddPreReadHistogramTime(uma_name.c_str(), time);
-  }
-#endif
-}
diff --git a/chrome/browser/browser_main.h b/chrome/browser/browser_main.h
index e4c1da21..c589a91 100644
--- a/chrome/browser/browser_main.h
+++ b/chrome/browser/browser_main.h
@@ -213,11 +213,4 @@ void ShowMissingLocaleMessageBox();
 // the UMA histogram |metric_name|.
 void RecordBrowserStartupTime();
 
-// Records a Startup category value to an UMA histogram in the context of the
-// PreReadExperiment field-trial. This will also report to the appropriate
-// Startup.HistogramName_PreRead(Enabled|Disabled) histogram as appropriate.
-// This is only called from OS_WIN specific code, so the implementation is
-// in browser_main_win.cc. This is a Windows specific experiment.
-void RecordPreReadExperimentTime(const char* name, base::TimeDelta time);
-
 #endif  // CHROME_BROWSER_BROWSER_MAIN_H_
diff --git a/chrome/browser/browser_main_win.cc b/chrome/browser/browser_main_win.cc
index 0d1306e..f4e971b 100644
--- a/chrome/browser/browser_main_win.cc
+++ b/chrome/browser/browser_main_win.cc
@@ -96,9 +96,12 @@ void RecordBrowserStartupTime() {
   ::GetProcessTimes(::GetCurrentProcess(), &creation_time, &ignore, &ignore,
       &ignore);
 
-  RecordPreReadExperimentTime(
+  UMA_HISTOGRAM_CUSTOM_TIMES(
       "Startup.BrowserMessageLoopStartTime",
-      base::Time::Now() - base::Time::FromFileTime(creation_time));
+      base::Time::Now() - base::Time::FromFileTime(creation_time),
+      base::TimeDelta::FromMilliseconds(1),
+      base::TimeDelta::FromHours(1),
+      100);
 }
 
 int AskForUninstallConfirmation() {