[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 d856c099036787ce4398938adb70bce6ff18c985..9ecf8bd6a1836a600904fc8c36eef7401208a162 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);
   virtual ~HotwordService();
 
-  // Overridden from content::NotificationObserver:
-  virtual void Observe(int type,
-                       const content::NotificationSource& source,
-                       const content::NotificationDetails& details) override;
-
   // Overridden from ExtensionRegisterObserver:
   virtual void OnExtensionInstalled(
       content::BrowserContext* browser_context,