[Media Galleries] Lazily initialize the storage monitor.

chrome/browser/extensions/api/media_galleries_private/gallery_watch_state_tracker.cc

Index: chrome/browser/extensions/api/media_galleries_private/gallery_watch_state_tracker.cc
diff --git a/chrome/browser/extensions/api/media_galleries_private/gallery_watch_state_tracker.cc b/chrome/browser/extensions/api/media_galleries_private/gallery_watch_state_tracker.cc
index e580d9cc2d3153a0de7d5e1697fe589d186e380e..e24823ec76e3f2a95eab60380a3d5f184f1818b4 100644
--- a/chrome/browser/extensions/api/media_galleries_private/gallery_watch_state_tracker.cc
+++ b/chrome/browser/extensions/api/media_galleries_private/gallery_watch_state_tracker.cc
@@ -72,18 +72,11 @@ const Extension* GetExtensionById(Profile* profile,
   return service->GetExtensionById(extension_id, false);
 }
 
-// Returns the initialized media galleries preferences for the specified
-// |profile|.
-chrome::MediaGalleriesPreferences* GetMediaGalleryPreferences(
-    Profile* profile) {
-  return g_browser_process->media_file_system_registry()->GetPreferences(
-      profile);
-}
-
 }  // namespace
 
 GalleryWatchStateTracker::GalleryWatchStateTracker(Profile* profile)
-    : profile_(profile) {
+    : profile_(profile),
+      preferences_(NULL) {

[Lei Zhang, 2013/05/14 22:32:00]

The ReadFromStorage() code will never be called if we don't do the notification
registration right below here. How about just making one GetPreferencesAsync()
call here, have registering for notifications as the callback, save the returned
value as |preferences_|, and get rid of SetPreferences?

[Greg Billock, 2013/05/15 01:42:56]

I'm not sure I understand. That call is being made externally, right? Won't it
happen as a result of these notifications? If we call GetPreferencesAsync here,
won't it just always load the storage monitor first thing, even if there's no
registered watchers?

   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
   DCHECK(profile_);
   registrar_.Add(this, chrome::NOTIFICATION_EXTENSION_LOADED,
@@ -160,6 +153,11 @@ void GalleryWatchStateTracker::RemoveAllGalleryWatchersForExtension(
   WriteToStorage(extension_id);
 }
 
+void GalleryWatchStateTracker::SetPreferences(
+    chrome::MediaGalleriesPreferences* preferences) {
+  preferences_ = preferences;
+}
+
 void GalleryWatchStateTracker::OnGalleryWatchAdded(
     const std::string& extension_id,
     chrome::MediaGalleryPrefId gallery_id) {
@@ -246,6 +244,20 @@ void GalleryWatchStateTracker::ReadFromStorage(const std::string& extension_id,
   if (!value.get() || !value->GetAsList(&list))
     return;
   chrome::MediaGalleryPrefIdSet gallery_ids = WatchedGalleryIdsFromValue(list);
+  if (gallery_ids.size() > 0) {
+    g_browser_process->media_file_system_registry()->GetPreferencesAsync(
+        profile_,
+        base::Bind(&GalleryWatchStateTracker::ReadFromStorageWithPreferences,
+                   AsWeakPtr(), extension_id, gallery_ids));
+  }
+}
+
+void GalleryWatchStateTracker::ReadFromStorageWithPreferences(
+    const std::string& extension_id,
+    chrome::MediaGalleryPrefIdSet gallery_ids,
+    chrome::MediaGalleriesPreferences* preferences) {
+  SetPreferences(preferences);
+
   for (chrome::MediaGalleryPrefIdSet::const_iterator id_iter =
            gallery_ids.begin();
        id_iter != gallery_ids.end(); ++id_iter) {
@@ -260,9 +272,9 @@ void GalleryWatchStateTracker::SetupGalleryWatch(
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
   const Extension* extension = GetExtensionById(profile_, extension_id);
   DCHECK(extension);
-  base::FilePath gallery_file_path(
-      GetMediaGalleryPreferences(profile_)->LookUpGalleryPathForExtension(
-          gallery_id, extension, false));
+  DCHECK(preferences_);
+  base::FilePath gallery_file_path(preferences_->LookUpGalleryPathForExtension(
+      gallery_id, extension, false));
   if (gallery_file_path.empty())
     return;
   MediaGalleriesPrivateEventRouter* router =
@@ -289,9 +301,9 @@ void GalleryWatchStateTracker::RemoveGalleryWatch(
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
   const Extension* extension = GetExtensionById(profile_, extension_id);
   DCHECK(extension);
-  base::FilePath gallery_file_path(
-      GetMediaGalleryPreferences(profile_)->LookUpGalleryPathForExtension(
-          gallery_id, extension, true));
+  DCHECK(preferences_);
+  base::FilePath gallery_file_path(preferences_->LookUpGalleryPathForExtension(
+      gallery_id, extension, true));
   if (gallery_file_path.empty())
     return;
   content::BrowserThread::PostTask(