[Hotword] Delay checking for audio devices until needed.

chrome/browser/search/hotword_service.h

 // Copyright 2013 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.
 
 #ifndef CHROME_BROWSER_SEARCH_HOTWORD_SERVICE_H_
 #define CHROME_BROWSER_SEARCH_HOTWORD_SERVICE_H_
 
 #include "base/basictypes.h"
 #include "base/memory/weak_ptr.h"
 #include "base/prefs/pref_change_registrar.h"
@@ skipping 14 matching lines @@
 }  // namespace extensions
 
 namespace hotword_internal {
 // Constants for the hotword field trial.
 extern const char kHotwordFieldTrialName[];
 extern const char kHotwordFieldTrialDisabledGroupName[];
 }  // namespace hotword_internal
 
 // 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.
   static bool DoesHotwordSupportLanguage(Profile* profile);
 
   // Returns true if the "enable-experimental-hotwording" flag is set.
   static bool IsExperimentalHotwordingEnabled();
 
   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,
                             bool is_update) override;
   void OnExtensionUninstalled(content::BrowserContext* browser_context,
                               const extensions::Extension* extension,
                               extensions::UninstallReason reason) override;
 
   // Checks for whether all the necessary files have downloaded to allow for
   // using the extension.
@@ skipping 83 matching lines @@
 
   base::WeakPtrFactory<HotwordService> weak_factory_;
 
   // Stores the launch mode for the Hotword Audio Verification App.
   LaunchMode hotword_audio_verification_launch_mode_;
 
   DISALLOW_COPY_AND_ASSIGN(HotwordService);
 };
 
 #endif  // CHROME_BROWSER_SEARCH_HOTWORD_SERVICE_H_