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

ios/public/provider/chrome/browser/voice/voice_search_prefs.cc

Index: ios/public/provider/chrome/browser/voice/voice_search_prefs.cc
diff --git a/ios/public/provider/chrome/browser/voice/voice_search_prefs.cc b/ios/public/provider/chrome/browser/voice/voice_search_prefs.cc
new file mode 100644
index 0000000000000000000000000000000000000000..57e9809dade52a9806b9802fbedebfd7e3b5ce08
--- /dev/null
+++ b/ios/public/provider/chrome/browser/voice/voice_search_prefs.cc
@@ -0,0 +1,15 @@
+// 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.
+
+#include "ios/public/provider/chrome/browser/voice/voice_search_prefs.h"
+
+namespace prefs {
+
+// User preferred speech input language for voice search.
+const char kVoiceSearchLocale[] = "ios.speechinput.voicesearch_locale";
+
+// Boolean which indicates if TTS after voice search is enabled.
+const char kVoiceSearchTTS[] = "ios.speechinput.voicesearch_tts";
+
+}  // namespace prefs