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_;

[xhwang, 2016/11/11 18:52:46]

It seems possible that is_closed_ is true but has_close_been_called_ is false,
e.g. when the CDM closed the session due to resource lost etc:

The CDM may close a session at any point, such as when the session is no longer
needed or when system resources are lost.

https://w3c.github.io/encrypted-media/#session-closed

We should document it clearly here since it's a bit tricky.

[jrummell, 2016/11/11 21:14:23]

Done.

 
+  // 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