Introduce a field trial for Instant.

chrome/browser/instant/instant_controller.cc

Index: chrome/browser/instant/instant_controller.cc
diff --git a/chrome/browser/instant/instant_controller.cc b/chrome/browser/instant/instant_controller.cc
index c25f62c1f046ce60793b5e27d925b8d9294dda9f..61738be980ccf30b958216d356f925735e7f0458 100644
--- a/chrome/browser/instant/instant_controller.cc
+++ b/chrome/browser/instant/instant_controller.cc
@@ -7,9 +7,11 @@
 #include "base/command_line.h"
 #include "base/message_loop.h"
 #include "base/metrics/histogram.h"
+#include "base/rand_util.h"
 #include "build/build_config.h"
 #include "chrome/browser/autocomplete/autocomplete_match.h"
 #include "chrome/browser/instant/instant_delegate.h"
+#include "chrome/browser/instant/instant_field_trial.h"
 #include "chrome/browser/instant/instant_loader.h"
 #include "chrome/browser/instant/instant_loader_manager.h"
 #include "chrome/browser/instant/promo_counter.h"
@@ -49,9 +51,10 @@ InstantController::InstantController(Profile* profile,
       last_transition_type_(PageTransition::LINK),
       ALLOW_THIS_IN_INITIALIZER_LIST(destroy_factory_(this)) {
   PrefService* service = profile->GetPrefs();
-  if (service) {
-    // kInstantWasEnabledOnce was added after instant, set it now to make sure
-    // it is correctly set.
+  if (service &&
+      InstantFieldTrial::GetGroup(profile) == InstantFieldTrial::INACTIVE) {
+    // kInstantEnabledOnce was added after instant, set it now to make sure it
+    // is correctly set.
     service->SetBoolean(prefs::kInstantEnabledOnce, true);
   }
 }
@@ -73,6 +76,9 @@ void InstantController::RegisterUserPrefs(PrefService* prefs) {
   prefs->RegisterInt64Pref(prefs::kInstantEnabledTime,
                            false,
                            PrefService::UNSYNCABLE_PREF);
+  prefs->RegisterDoublePref(prefs::kInstantFieldTrialRandomDraw,
+                            base::RandDouble(),
+                            PrefService::UNSYNCABLE_PREF);
   PromoCounter::RegisterUserPrefs(prefs, prefs::kInstantPromo);
 }
 
@@ -100,7 +106,8 @@ void InstantController::RecordMetrics(Profile* profile) {
 // static
 bool InstantController::IsEnabled(Profile* profile) {
   PrefService* prefs = profile->GetPrefs();
-  return prefs->GetBoolean(prefs::kInstantEnabled);
+  return prefs->GetBoolean(prefs::kInstantEnabled) ||
+         InstantFieldTrial::IsExperimentGroup(profile);
 }
 
 // static
@@ -135,6 +142,13 @@ void InstantController::Disable(Profile* profile) {
                                 delta.InMinutes(), 1, 60 * 24 * 10, 50);
   }
 
+  if (InstantFieldTrial::IsExperimentGroup(profile)) {
+    UMA_HISTOGRAM_COUNTS(
+        "Instant.FieldTrialOptOut." + InstantFieldTrial::GetGroupName(profile),
+        1);
+  }
+
+  service->SetBoolean(prefs::kInstantEnabledOnce, true);
   service->SetBoolean(prefs::kInstantEnabled, false);
 }
 
@@ -376,8 +390,10 @@ void InstantController::OnAutocompleteLostFocus(
 void InstantController::OnAutocompleteGotFocus(
     TabContentsWrapper* tab_contents) {
   CommandLine* cl = CommandLine::ForCurrentProcess();
-  if (!cl->HasSwitch(switches::kPreloadInstantSearch))
+  if (!cl->HasSwitch(switches::kPreloadInstantSearch) &&
+      !InstantFieldTrial::IsExperimentGroup(tab_contents->profile())) {
     return;
+  }
 
   if (is_active_)
     return;
@@ -704,7 +720,8 @@ InstantController::PreviewCondition InstantController::GetPreviewConditionFor(
     return PREVIEW_CONDITION_BLACKLISTED;
 
   const CommandLine* cl = CommandLine::ForCurrentProcess();
-  if (cl->HasSwitch(switches::kRestrictInstantToSearch) &&
+  if ((cl->HasSwitch(switches::kRestrictInstantToSearch) ||
+       InstantFieldTrial::IsExperimentGroup(tab_contents_->profile())) &&
       match.type != AutocompleteMatch::SEARCH_WHAT_YOU_TYPED &&
       match.type != AutocompleteMatch::SEARCH_HISTORY &&
       match.type != AutocompleteMatch::SEARCH_SUGGEST &&