Adds a skeleton component app for Always-On Hotwording opt-in flow.

chrome/browser/search/hotword_service.h

Index: chrome/browser/search/hotword_service.h
diff --git a/chrome/browser/search/hotword_service.h b/chrome/browser/search/hotword_service.h
index 8d6862d8d59c6fec2d55fe468a2abe4bbf08420e..c871684914afe3c20f7e257e368548e21c7edfd6 100644
--- a/chrome/browser/search/hotword_service.h
+++ b/chrome/browser/search/hotword_service.h
@@ -76,6 +76,10 @@ class HotwordService : public content::NotificationObserver,
   void EnableHotwordExtension(ExtensionService* extension_service);
   void DisableHotwordExtension(ExtensionService* extension_service);
 
+  // Handles launching the Hotword Audio Verification extension when the user
+  // turns it on via the settings menu.
+  void OnHotwordAlwaysOnSearchEnabledChanged(const std::string& pref_name);
+
   // Handles enabling/disabling the hotword extension when the user
   // turns it off via the settings menu.
   void OnHotwordSearchEnabledChanged(const std::string& pref_name);