Revert of Enable gallery watches on Mac

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 a7b4e72d278470f58057a9b60f441d36ead8d90c..8055025b7d766c960be009bb79dceffe9f7513e8 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
@@ -92,12 +92,15 @@
 GalleryWatchStateTracker* GalleryWatchStateTracker::GetForProfile(
     Profile* profile) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+#if defined(OS_WIN) || defined(OS_LINUX)
+  // Gallery watch operation is not supported on Mac: crbug.com/144491.
   DCHECK(profile);
   MediaGalleriesPrivateAPI* private_api =
       MediaGalleriesPrivateAPI::Get(profile);
   // In unit tests, we don't have a MediaGalleriesPrivateAPI.
   if (private_api)
     return private_api->GetGalleryWatchStateTracker();
+#endif
   return NULL;
 }