[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) {
   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;

[Lei Zhang, 2013/05/15 22:44:31]

Make this a no-op if |preferences_| is already set?

[Greg Billock, 2013/05/16 01:59:58]

Actually, this is important. Will the tracker be used across profiles? If so, we
need a different strategy than I have here. If there's one per profile, it'll
work OK. The constructor takes a profile, so that makes it seem like the answer
is no, it's per-profile.

I'll set the code to assume this.

[Lei Zhang, 2013/05/16 03:35:21]

The tracker object is only used by the media gallery api object, which is per
profile.

+}
+
 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) {

[Lei Zhang, 2013/05/15 22:44:31]

You can use set::empty() instead.

[Greg Billock, 2013/05/16 01:59:58]

Done.

+    g_browser_process->media_file_system_registry()->GetPreferencesAsync(

[Lei Zhang, 2013/05/15 22:44:31]

How about we check |preferences_|, and if it is already set, then just call
ReadFromStorageWithPreferences() directly?

[Greg Billock, 2013/05/16 01:59:58]

I'd rather always use the same access path -- this will call the callback in the
same stack if it is already set.

+        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(