media: Avoid access violation in MojoCdm after connection error

media/base/cdm_session_tracker.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/base/cdm_session_tracker.h"
 
 namespace media {
 
 CdmSessionTracker::CdmSessionTracker() {}
 
 CdmSessionTracker::~CdmSessionTracker() {
-  DCHECK(session_ids_.empty());
+  DCHECK(!HasRemainingSessions());
 }
 
 void CdmSessionTracker::AddSession(const std::string& session_id) {
   DCHECK(session_ids_.find(session_id) == session_ids_.end());
   session_ids_.insert(session_id);
 }
 
 void CdmSessionTracker::RemoveSession(const std::string& session_id) {
   auto it = session_ids_.find(session_id);
   DCHECK(it != session_ids_.end());
   session_ids_.erase(it);
 }
 
 void CdmSessionTracker::CloseRemainingSessions(
     const SessionClosedCB& session_closed_cb) {
   std::unordered_set<std::string> session_ids;
   session_ids.swap(session_ids_);
 
   for (const auto& session_id : session_ids)
     session_closed_cb.Run(session_id);
 }
 
+bool CdmSessionTracker::HasRemainingSessions() const {
+  return !session_ids_.empty();
+}
+
 }  // namespace media