media: Avoid access violation in MojoCdm after connection error

media/base/cdm_session_tracker.h

Index: media/base/cdm_session_tracker.h
diff --git a/media/base/cdm_session_tracker.h b/media/base/cdm_session_tracker.h
index c72e25c72b40508438885f3e26e47fa5e0b9e305..98cfbbc0b25c1743647688ca421d16c75dafb448 100644
--- a/media/base/cdm_session_tracker.h
+++ b/media/base/cdm_session_tracker.h
@@ -22,16 +22,19 @@ class MEDIA_EXPORT CdmSessionTracker {
   CdmSessionTracker();
   ~CdmSessionTracker();
 
-  // Add |session_id| to the list of sessions being tracked.
+  // Adds |session_id| to the list of sessions being tracked.
   void AddSession(const std::string& session_id);
 
-  // Remove |session_id| from the list of sessions being tracked.
+  // Removes |session_id| from the list of sessions being tracked.
   void RemoveSession(const std::string& session_id);
 
-  // Call |session_closed_cb| on any remaining sessions in the list and then
+  // Calls |session_closed_cb| on any remaining sessions in the list and then
   // clear the list.
   void CloseRemainingSessions(const SessionClosedCB& session_closed_cb);
 
+  // Returns whether there are any remaining sessions being tracked.
+  bool HasRemainingSessions() const;
+
  private:
   std::unordered_set<std::string> session_ids_;