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..6b5f40734df8a20c96f8b28852899d8495312c2a 100644
--- a/chrome/browser/instant/instant_controller.cc
+++ b/chrome/browser/instant/instant_controller.cc
@@ -10,6 +10,7 @@
 #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 +50,9 @@ 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 && !instant_field_trial::IsExperiment(profile)) {
+    // kInstantEnabledOnce was added after instant, set it now to make sure it
+    // is correctly set.
     service->SetBoolean(prefs::kInstantEnabledOnce, true);
   }
 }
@@ -100,7 +101,8 @@ 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) ||
+         instant_field_trial::IsExperiment(profile);
 }
 
 // static
@@ -704,7 +706,8 @@ InstantController::PreviewCondition InstantController::GetPreviewConditionFor(
     return PREVIEW_CONDITION_BLACKLISTED;
 
   const CommandLine* cl = CommandLine::ForCurrentProcess();
-  if (cl->HasSwitch(switches::kRestrictInstantToSearch) &&
+  if ((cl->HasSwitch(switches::kRestrictInstantToSearch) ||
+       instant_field_trial::IsExperiment(tab_contents_->profile())) &&
       match.type != AutocompleteMatch::SEARCH_WHAT_YOU_TYPED &&
       match.type != AutocompleteMatch::SEARCH_HISTORY &&
       match.type != AutocompleteMatch::SEARCH_SUGGEST &&