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..b6f05f543de36b23e5f4c1c592f5f76e0033d6f5 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -707,7 +707,6 @@ 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);
@@ -716,29 +715,6 @@ void ChromeBrowserMainParts::RecordPreReadExperimentTime(const char* name,
   // the UMA_HISTOGRAM_CUSTOM_TIMES macro--it uses a static variable, and the
   // first call wins.
   AddPreReadHistogramTime(name, time);

[Roger McFarlane (Chromium), 2013/08/29 15:28:37]

As this function has now been reduced to nothing, should it be clobbered and the
call-sites updated to directly call AddPreREadHistogramTime()? Could the
call-sites even just be updated to use UMA_HISTOGRAM_*?

[Alexei Svitkine (slow), 2013/08/29 17:44:05]

I agree, it should just be replaced with an equivalent UMA_HISTOGRAM_*() macro
call.

[Roger McFarlane (Chromium), 2013/08/30 21:27:37]

Done.

-
-#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
 }
 
 // -----------------------------------------------------------------------------