Use an experiment value to set the instant_extended.enabled pref default.

chrome/browser/ui/browser_instant_controller.cc

Index: chrome/browser/ui/browser_instant_controller.cc
diff --git a/chrome/browser/ui/browser_instant_controller.cc b/chrome/browser/ui/browser_instant_controller.cc
index 7abe3aa900015a2cc93088f32a243fdf112b7983..4118de59b0de8e390a68fa3136e01b1275fbafad 100644
--- a/chrome/browser/ui/browser_instant_controller.cc
+++ b/chrome/browser/ui/browser_instant_controller.cc
@@ -72,10 +72,27 @@ bool BrowserInstantController::IsInstantEnabled(Profile* profile) {
 void BrowserInstantController::RegisterUserPrefs(PrefServiceSyncable* prefs) {
   prefs->RegisterBooleanPref(prefs::kInstantConfirmDialogShown, false,
                              PrefServiceSyncable::SYNCABLE_PREF);
-  prefs->RegisterBooleanPref(prefs::kInstantExtendedEnabled, true,
-                             PrefServiceSyncable::SYNCABLE_PREF);
   prefs->RegisterBooleanPref(prefs::kInstantEnabled, false,
                              PrefServiceSyncable::SYNCABLE_PREF);
+
+  search::InstantExtendedDefault instant_extended_default_setting =
+      search::GetInstantExtendedDefaultSetting();
+
+  bool instant_extended_value = true;
+  switch (instant_extended_default_setting) {
+    case search::INSTANT_FORCE_ON:
+      break;
+    case search::INSTANT_USE_EXISTING:
+      instant_extended_value = prefs->GetBoolean(prefs::kInstantEnabled);
+      break;
+    case search::INSTANT_FORCE_OFF:
+      instant_extended_value = false;
+      break;
+  }
+
+  prefs->RegisterBooleanPref(prefs::kInstantExtendedEnabled,
+                             instant_extended_value,
+                             PrefServiceSyncable::SYNCABLE_PREF);
 }
 
 bool BrowserInstantController::OpenInstant(WindowOpenDisposition disposition) {