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

ios/public/provider/chrome/browser/voice/voice_search_provider.mm

Index: ios/public/provider/chrome/browser/voice/voice_search_provider.mm
diff --git a/ios/public/provider/chrome/browser/voice/voice_search_provider.mm b/ios/public/provider/chrome/browser/voice/voice_search_provider.mm
index 45f175280218419b1e4b46c4218821cac5275214..3bef6f0544e6ac721c38a395d38ce482d318ce69 100644
--- a/ios/public/provider/chrome/browser/voice/voice_search_provider.mm
+++ b/ios/public/provider/chrome/browser/voice/voice_search_provider.mm
@@ -4,10 +4,18 @@
 
 #import "ios/public/provider/chrome/browser/voice/voice_search_provider.h"
 
+#import "ios/public/provider/chrome/browser/voice/voice_search_controller.h"
+
 NSArray* VoiceSearchProvider::GetAvailableLanguages() const {
   return @[];
 }
 
 AudioSessionController* VoiceSearchProvider::GetAudioSessionController() const {
-  return nil;
+  return nullptr;
+}
+
+scoped_refptr<VoiceSearchController>
+VoiceSearchProvider::CreateVoiceSearchController(
+    ios::ChromeBrowserState* browser_state) const {
+  return scoped_refptr<VoiceSearchController>(nullptr);
 }