Remove DCHECK in DialRegistry dtor. This may trigger on browser shutdown if

chrome/browser/extensions/api/dial/dial_api.h

Index: chrome/browser/extensions/api/dial/dial_api.h
diff --git a/chrome/browser/extensions/api/dial/dial_api.h b/chrome/browser/extensions/api/dial/dial_api.h
index 6548a72badda55ff325789dbb2d2dc57a300ab4f..51f0f55aabdc9a84c4e5cbc965ad3527add4a601 100644
--- a/chrome/browser/extensions/api/dial/dial_api.h
+++ b/chrome/browser/extensions/api/dial/dial_api.h
@@ -21,6 +21,10 @@ class DialRegistry;
 // the DIAL registry. It takes care of creating the registry on the IO thread
 // and is an observer of the registry. It makes sure devices events are sent out
 // to extension listeners on the right thread.
+//
+// TODO(mfoltz): This should probably inherit from BrowserContextKeyedAPI
+// instead; ShutdownOnUIThread below is a no-op, which is the whole point of
+// RefcountedKeyedService.
 class DialAPI : public RefcountedKeyedService,
                 public EventRouter::Observer,
                 public DialRegistry::Observer {