[Media Galleries] Lazily initialize the storage monitor.

chrome/browser/media_galleries/media_file_system_registry.cc

Index: chrome/browser/media_galleries/media_file_system_registry.cc
diff --git a/chrome/browser/media_galleries/media_file_system_registry.cc b/chrome/browser/media_galleries/media_file_system_registry.cc
index e659ad7431d11df61bf904f0e98077d6a3cead7e..70d9e4d36793ee29535742844af3984614c1d74a 100644
--- a/chrome/browser/media_galleries/media_file_system_registry.cc
+++ b/chrome/browser/media_galleries/media_file_system_registry.cc
@@ -435,7 +435,18 @@ void MediaFileSystemRegistry::GetMediaFileSystemsForExtension(
 
   Profile* profile =
       Profile::FromBrowserContext(rvh->GetProcess()->GetBrowserContext());
-  MediaGalleriesPreferences* preferences = GetPreferences(profile);
+  GetPreferencesAsync(
+      profile, base::Bind(
+          &MediaFileSystemRegistry::GetMediaFileSystemsPostStorageMonitorInit,
+          base::Unretained(this),
+          rvh, extension, callback));
+}
+
+void MediaFileSystemRegistry::GetMediaFileSystemsPostStorageMonitorInit(
+    const content::RenderViewHost* rvh,
+    const extensions::Extension* extension,
+    const MediaFileSystemsCallback& callback,
+    MediaGalleriesPreferences* preferences) {
   MediaGalleryPrefIdSet galleries =
       preferences->GalleriesForExtension(*extension);
 
@@ -444,6 +455,8 @@ void MediaFileSystemRegistry::GetMediaFileSystemsForExtension(
     return;
   }
 
+  Profile* profile =
+      Profile::FromBrowserContext(rvh->GetProcess()->GetBrowserContext());
   if (!ContainsKey(pref_change_registrar_map_, profile)) {
     PrefChangeRegistrar* pref_registrar = new PrefChangeRegistrar;
     pref_registrar->Init(profile->GetPrefs());
@@ -470,6 +483,34 @@ void MediaFileSystemRegistry::GetMediaFileSystemsForExtension(
                                       callback);
 }
 
+void MediaFileSystemRegistry::GetPreferencesAsync(
+    Profile* profile,
+    base::Callback<void(MediaGalleriesPreferences*)> callback) {
+  StorageMonitor* monitor = StorageMonitor::GetInstance();

[tommycli, 2013/05/10 17:41:24]

I see that StorageMonitor::GetInstance() is called in many other places, but
this is the only place Init is called.

Does this mean that this piece of code is guaranteed to run before all other
calls to GetInstance? If so, I think GetInstance should be DCHECKed to make sure
it's initialized.

The first initialization here could be done with a static function.

[Greg Billock, 2013/05/10 17:58:27]

Yes. I have a long-term goal to reduce/eliminate that global, but that'll take
more time.
Yes, that's the expectation. It's kind of risky, so please let me know if there
are gaps. I'm not planning to check this in until I have more DCHECKs in place
to validate this assumption.
It's legal to do some things (register for notifications, for instance), but not
others. So that's a problem we don't have a great solution for. :-/

+  if (!monitor) {
+    callback.Run(MediaGalleriesPreferencesFactory::GetForProfile(profile));
+    return;
+  }
+
+  if (monitor->IsInitialized()) {
+    callback.Run(GetPreferences(profile));
+    return;
+  }
+
+  monitor->Initialize(
+      base::Bind(&MediaFileSystemRegistry::OnStorageMonitorInitialized,
+                 base::Unretained(this),

[Lei Zhang, 2013/05/11 02:12:23]

I would probably feel better about this Unretained() if we can guarantee
MediaFileSystemRegistry outlives StorageMonitor. I feel StorageMonitor is a more
low level object, so there's no guarantee MediaFileSystemRegistry outlives
StorageMonitor.

[Greg Billock, 2013/05/13 21:20:38]

Shall we add a weak ptr factory?

+                 profile, callback));
+
+  // TODO(gbillock): set a timeout here to bail out of init?
+}
+
+void MediaFileSystemRegistry::OnStorageMonitorInitialized(
+    Profile* profile,
+    base::Callback<void(MediaGalleriesPreferences*)> callback) {
+  callback.Run(GetPreferences(profile));
+}
+
 MediaGalleriesPreferences* MediaFileSystemRegistry::GetPreferences(
     Profile* profile) {
   MediaGalleriesPreferences* preferences =
@@ -486,6 +527,7 @@ MediaGalleriesPreferences* MediaFileSystemRegistry::GetPreferences(
   StorageMonitor* monitor = StorageMonitor::GetInstance();
   if (!monitor)
     return preferences;
+  DCHECK(monitor->IsInitialized());
   std::vector<StorageInfo> existing_devices = monitor->GetAttachedStorage();
   for (size_t i = 0; i < existing_devices.size(); i++) {
     if (!MediaStorageUtil::IsMediaDevice(existing_devices[i].device_id))