[Hotword] Delay checking for audio devices until needed.

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 3a70003bdbfbf9323c690033ce4ed5518e1b8a71..79e22d968d350c8ef0c6bdfdf0234851db210174 100644
--- a/chrome/browser/search/hotword_service.h
+++ b/chrome/browser/search/hotword_service.h
@@ -32,8 +32,7 @@ extern const char kHotwordFieldTrialDisabledGroupName[];
 
 // Provides an interface for the Hotword component that does voice triggered
 // search.
-class HotwordService : public content::NotificationObserver,
-                       public extensions::ExtensionRegistryObserver,
+class HotwordService : public extensions::ExtensionRegistryObserver,
                        public KeyedService {
  public:
   // Returns true if the hotword supports the current system language.
@@ -45,11 +44,6 @@ class HotwordService : public content::NotificationObserver,
   explicit HotwordService(Profile* profile);
   ~HotwordService() override;
 
-  // Overridden from content::NotificationObserver:
-  void Observe(int type,
-               const content::NotificationSource& source,
-               const content::NotificationDetails& details) override;
-
   // Overridden from ExtensionRegisterObserver:
   void OnExtensionInstalled(content::BrowserContext* browser_context,
                             const extensions::Extension* extension,