EME: Make sure sessions are closed before they are destroyed

media/blink/webcontentdecryptionmodulesession_impl.h

Index: media/blink/webcontentdecryptionmodulesession_impl.h
diff --git a/media/blink/webcontentdecryptionmodulesession_impl.h b/media/blink/webcontentdecryptionmodulesession_impl.h
index 18db47265a4c1cb093b59daf4893c4bbd2f34c3e..595582beaa54e202eff63a30e64c0120186f3d13 100644
--- a/media/blink/webcontentdecryptionmodulesession_impl.h
+++ b/media/blink/webcontentdecryptionmodulesession_impl.h
@@ -80,6 +80,9 @@ class WebContentDecryptionModuleSessionImpl
   // closed() event.
   bool is_closed_;
 
+  // Keep track of whether close() has been called on this session.
+  bool has_close_been_called_;
+
   base::ThreadChecker thread_checker_;
   // Since promises will live until they are fired, use a weak reference when
   // creating a promise in case this class disappears before the promise