[Media Gallery] Add existing attached devices to the prefs in time for media galleries dialog.

chrome/browser/media_gallery/media_galleries_preferences_factory.h

Index: chrome/browser/media_gallery/media_galleries_preferences_factory.h
diff --git a/chrome/browser/media_gallery/media_galleries_preferences_factory.h b/chrome/browser/media_gallery/media_galleries_preferences_factory.h
index 174068018589c4be8703652b10feb945926356cb..48e370fb0b4f6cf9d5915800a892f4130e63b35a 100644
--- a/chrome/browser/media_gallery/media_galleries_preferences_factory.h
+++ b/chrome/browser/media_gallery/media_galleries_preferences_factory.h
@@ -19,6 +19,8 @@ class MediaGalleriesPreferences;
 // Profiles.
 class MediaGalleriesPreferencesFactory : public ProfileKeyedServiceFactory {
  public:
+  // Use MediaFileSystemRegistry::GetProfilePreferences() to get
+  // MediaGalleriesPreferences.
   static chrome::MediaGalleriesPreferences* GetForProfile(Profile* profile);
 
   static MediaGalleriesPreferencesFactory* GetInstance();