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

ios/chrome/browser/voice/voice_search_prefs_registration.h

Index: ios/chrome/browser/voice/voice_search_prefs_registration.h
diff --git a/ios/chrome/browser/voice/voice_search_prefs_registration.h b/ios/chrome/browser/voice/voice_search_prefs_registration.h
new file mode 100644
index 0000000000000000000000000000000000000000..d347f49169903cde9315eefc8f969739361cbd3e
--- /dev/null
+++ b/ios/chrome/browser/voice/voice_search_prefs_registration.h
@@ -0,0 +1,16 @@
+// Copyright 2016 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.
+
+#ifndef IOS_CHROME_BROWSER_VOICE_VOICE_SEARCH_PREFS_REGISTRATION_H_
+#define IOS_CHROME_BROWSER_VOICE_VOICE_SEARCH_PREFS_REGISTRATION_H_
+
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
+// Registers the prefs needed by voice search.
+void RegisterVoiceSearchBrowserStatePrefs(
+    user_prefs::PrefRegistrySyncable* registry);
+
+#endif  // IOS_CHROME_BROWSER_VOICE_VOICE_SEARCH_PREFS_REGISTRATION_H_