Make a channel and time limited persistent PreRead experiment

chrome/browser/browser_main.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 <algorithm>
 #include <string>
 #include <vector>
 
@@ skipping 147 matching lines @@
 // TODO(port): several win-only methods have been pulled out of this, but
 // BrowserMain() as a whole needs to be broken apart so that it's usable by
 // other platforms. For now, it's just a stub. This is a serious work in
 // progress and should not be taken as an indication of a real refactoring.
 
 #if defined(OS_WIN)
 #include <windows.h>
 #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"
 #include "chrome/browser/browser_util_win.h"
 #include "chrome/browser/first_run/try_chrome_dialog_view.h"
 #include "chrome/browser/first_run/upgrade_util_win.h"
 #include "chrome/browser/net/url_fixer_upper.h"
 #include "chrome/browser/rlz/rlz.h"
 #include "chrome/browser/ui/views/user_data_dir_dialog.h"
 #include "chrome/installer/util/helper.h"
@@ skipping 629 matching lines @@
   CHECK(metrics_reporting_enabled);
   bool breakpad_enabled =
       local_state->GetBoolean(prefs::kMetricsReportingEnabled);
   if (!breakpad_enabled && metrics_reporting_enabled->IsUserModifiable())
     breakpad_enabled = getenv(env_vars::kHeadless) != NULL;
 #endif  // #if defined(OS_CHROMEOS)
   return breakpad_enabled;
 }
 #endif  // #if defined(USE_LINUX_BREAKPAD)
 
+// 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);
+}
+
 }  // namespace
 
 namespace chrome_browser {
 // This error message is not localized because we failed to load the
 // localization data files.
 const char kMissingLocaleDataTitle[] = "Missing File Error";
 const char kMissingLocaleDataMessage[] =
     "Unable to find locale data files. Please reinstall.";
 }  // namespace chrome_browser
 
@@ skipping 1219 matching lines @@
       upgrade_util::SaveLastModifiedTimeOfExe();
 #endif
 
       // Record now as the last successful chrome start.
       GoogleUpdateSettings::SetLastRunTime();
       // Call Recycle() here as late as possible, before going into the loop
       // because Start() will add things to it while creating the main window.
       if (pool)
         pool->Recycle();
 
-      UMA_HISTOGRAM_CUSTOM_TIMES(
-          "Startup.BrowserOpenTabs",
-          base::TimeTicks::Now() - browser_open_start,
-          base::TimeDelta::FromMilliseconds(1),
-          base::TimeDelta::FromHours(1),
-          100);
+      RecordPreReadExperimentTime("Startup.BrowserOpenTabs",
+                                  base::TimeTicks::Now() - browser_open_start);
 
       // TODO(mad): Move this call in a proper place on CrOS.
       // http://crosbug.com/17687
 #if !defined(OS_CHROMEOS)
       // If we're running tests (ui_task is non-null), then we don't want to
       // call FetchLanguageListFromTranslateServer
       if (parameters.ui_task == NULL && translate_manager != NULL) {
         // TODO(willchan): Get rid of this after TranslateManager doesn't use
         // the default request context. http://crbug.com/89396.
         // This is necessary to force |default_request_context_| to be
@@ skipping 74 matching lines @@
 #if defined(OS_CHROMEOS)
   // To be precise, logout (browser shutdown) is not yet done, but the
   // remaining work is negligible, hence we say LogoutDone here.
   chromeos::BootTimesLoader::Get()->AddLogoutTimeMarker("LogoutDone",
                                                         false);
   chromeos::BootTimesLoader::Get()->WriteLogoutTimes();
 #endif
   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)
+  // The pre-read experiment is Windows 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;
+  if (env->GetVar(chrome::kPreReadEnvironmentVariable, &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
+}
+