Add one-time randomization support for FieldTrial, and the ability to

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 1306 matching lines @@
 
   // Initialize thread watcher system. This is a singleton and is used by
   // WatchDogThread to keep track of information about threads that are being
   // watched.
   scoped_ptr<ThreadWatcherList> thread_watcher_list(new ThreadWatcherList());
 
   // Convert active labs into switches. Modifies the current command line.
   about_flags::ConvertFlagsToSwitches(local_state,
                                       CommandLine::ForCurrentProcess());
 
-  // Now the command line has been mutated based on about:flags, we can run some
-  // field trials
+  // Must initialize metrics after labs have been converted into switches,
+  // but before field trials are set up (so that client ID is available for
+  // one-time randomized field trials).
+  MetricsService* metrics = InitializeMetrics(parsed_command_line, local_state);

[jar (doing other things), 2011/04/29 00:57:11]

This will probably work.  I'm always nervous about moving much around at startup
time.  There is always the sad chance that we'll change dll load ordering or
such.  Be sure to watch the startup perf dashboard as you land with this change.

[Jói, 2011/05/02 18:55:03]

I will watch the startup perf dash.

[Jói, 2011/05/05 15:07:39]

Just to confirm, I looked in detail at every Startup/New Tab Cold/New Tab Warm
perf chart and there is nothing to indicate this change slowed things down.  I
also glanced over the rest of the perf dashboard, again no indication of a
slowdown.

Cheers,
Jói

+
+  // Initialize FieldTrialList to support FieldTrials that use one-time
+  // randomization.  The client ID will be empty if the user has not opted
+  // to send metrics.
+  std::string client_id = metrics->GetClientId();
+  if (!client_id.empty())
+    base::FieldTrialList::EnableOneTimeRandomization(client_id);
+
+  // Now the command line has been mutated based on about:flags, and one-time
+  // randomization has been enabled, we can run some field trials
   parts->SetupFieldTrials();

[jar (doing other things), 2011/04/29 00:57:11]

Wouldn't lines 1327-1337 fit nicely into SetupFieldTrials()?

Note that this function always grows bigger and bigger... and folks keep trying
to factor out sections.  It sure seems like the initialization should fit nicely
in there.

[Jói, 2011/05/02 18:55:03]

Good point.  I've factored it out.

 
   // Now that all preferences have been registered, set the install date
   // for the uninstall metrics if this is our first run. This only actually
   // gets used if the user has metrics reporting enabled at uninstall time.
   int64 install_date =
       local_state->GetInt64(prefs::kUninstallMetricsInstallDate);
   if (install_date == 0) {
     local_state->SetInt64(prefs::kUninstallMetricsInstallDate,
                           base::Time::Now().ToTimeT());
   }
@@ skipping 323 matching lines @@
     sdch_trial->AppendGroup("global_disable_sdch",
                             kSDCH_DISABLE_PROBABILITY);
     if (sdch_enabled != sdch_trial->group())
       sdch_supported_domain = "never_enabled_sdch_for_any_domain";
   }
 
   net::SdchManager sdch_manager;  // Singleton database.
   sdch_manager.set_sdch_fetcher(new SdchDictionaryFetcher);
   sdch_manager.EnableSdchSupport(sdch_supported_domain);
 
-  MetricsService* metrics = InitializeMetrics(parsed_command_line, local_state);
   InstallJankometer(parsed_command_line);
 
 #if defined(OS_WIN) && !defined(GOOGLE_CHROME_BUILD)
   if (parsed_command_line.HasSwitch(switches::kDebugPrint)) {
     FilePath path =
         parsed_command_line.GetSwitchValuePath(switches::kDebugPrint);
     printing::PrintedDocument::set_debug_dump_path(path);
   }
 #endif
 
@@ skipping 204 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("BrowserMain", 0, 0);
   return result_code;
 }