[ios] Adds a VoiceSearchController interface to the provider layer.

ios/chrome/browser/prefs/browser_prefs.mm

Index: ios/chrome/browser/prefs/browser_prefs.mm
diff --git a/ios/chrome/browser/prefs/browser_prefs.mm b/ios/chrome/browser/prefs/browser_prefs.mm
index 506b63ce897370fe5ec95ac078b6346555a6f31a..4c7e6386b0103b20c68178d1d87318ceddc7a057 100644
--- a/ios/chrome/browser/prefs/browser_prefs.mm
+++ b/ios/chrome/browser/prefs/browser_prefs.mm
@@ -40,6 +40,7 @@
 #include "ios/chrome/browser/notification_promo.h"
 #include "ios/chrome/browser/pref_names.h"
 #include "ios/chrome/browser/signin/signin_manager_factory.h"
+#include "ios/chrome/browser/voice/voice_search_prefs_registration.h"
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 #include "ui/base/l10n/l10n_util.h"
 
@@ -95,6 +96,7 @@ void RegisterBrowserStatePrefs(user_prefs::PrefRegistrySyncable* registry) {
   translate::TranslatePrefs::RegisterProfilePrefs(registry);
   variations::VariationsService::RegisterProfilePrefs(registry);
   ZeroSuggestProvider::RegisterProfilePrefs(registry);
+  RegisterVoiceSearchBrowserStatePrefs(registry);
 
   registry->RegisterBooleanPref(prefs::kDataSaverEnabled, false);
   registry->RegisterBooleanPref(