Re-enable pre-read experiment as a finch field trial.

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
diff --git a/chrome/browser/chrome_browser_main.cc b/chrome/browser/chrome_browser_main.cc
index e8612a18a4d7a25953c8afaf9187d781462b4dd1..f96917a0a34024a5d98c2927d0869e7c6e4296aa 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -366,20 +366,6 @@ OSStatus KeychainCallback(SecKeychainEvent keychain_event,
 }
 #endif
 
-// 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::HistogramBase* counter = base::Histogram::FactoryTimeGet(
-      name, kMin, kMax, kBuckets, base::Histogram::kUmaTargetedHistogramFlag);
-
-  counter->AddTime(time);
-}
-
 void RegisterComponentsForUpdate(const CommandLine& command_line) {
   ComponentUpdateService* cus = g_browser_process->component_updater();
 
@@ -695,8 +681,8 @@ void ChromeBrowserMainParts::RecordBrowserStartupTime() {
       base::CurrentProcessInfo::CreationTime();
 
   if (!is_first_run && !process_creation_time.is_null()) {
-    RecordPreReadExperimentTime("Startup.BrowserMessageLoopStartTime",
-        base::Time::Now() - process_creation_time);
+    base::TimeDelta delay = base::Time::Now() - process_creation_time;
+    UMA_HISTOGRAM_LONG_TIMES_100("Startup.BrowserMessageLoopStartTime", delay);
   }
 #endif  // defined(OS_MACOSX) || defined(OS_WIN) || defined(OS_LINUX)
 
@@ -707,40 +693,6 @@ void ChromeBrowserMainParts::RecordBrowserStartupTime() {
   new LoadCompleteListener();
 }
 
-// This code is specific to the Windows-only PreReadExperiment field-trial.
-void ChromeBrowserMainParts::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)
-#if defined(GOOGLE_CHROME_BUILD)
-  // The pre-read experiment is Windows and Google Chrome specific.
-  scoped_ptr<base::Environment> env(base::Environment::Create());
-
-  // Only record the sub-histogram result if the experiment is running
-  // (environment variable is set, and valid).
-  std::string pre_read_percentage;
-  if (env->GetVar(chrome::kPreReadEnvironmentVariable, &pre_read_percentage)) {
-    std::string uma_name(name);
-
-    // We want XP to record a separate histogram, as the loader on XP
-    // is very different from the Vista and Win7 loaders.
-    if (base::win::GetVersion() <= base::win::VERSION_XP)
-      uma_name += "_XP";
-
-    uma_name += "_PreRead_";
-    uma_name += pre_read_percentage;
-    AddPreReadHistogramTime(uma_name.c_str(), time);
-  }
-#endif
-#endif
-}
-
 // -----------------------------------------------------------------------------
 // TODO(viettrungluu): move more/rest of BrowserMain() into BrowserMainParts.
 
@@ -1553,8 +1505,9 @@ int ChromeBrowserMainParts::PreMainMessageLoopRunImpl() {
       parameters().autorelease_pool->Recycle();
 #endif
 
-    RecordPreReadExperimentTime("Startup.BrowserOpenTabs",
-                                base::TimeTicks::Now() - browser_open_start);
+    base::TimeTicks browser_open_end = base::TimeTicks::Now();
+    base::TimeDelta browser_open_delta = browser_open_end - browser_open_start;

[Alexei Svitkine (slow), 2013/09/03 18:48:45]

Nit: Inline base::TimeTicks::Now(), e.g.:

    base::TimeDelta startup_time = base::TimeTicks::Now() - browser_open_start;

[Roger McFarlane (Chromium), 2013/09/03 19:32:10]

Done.

+    UMA_HISTOGRAM_LONG_TIMES_100("Startup.BrowserOpenTabs", browser_open_delta);
 
     // If we're running tests (ui_task is non-null), then we don't want to
     // call FetchLanguageListFromTranslateServer or