Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/media/user_media_client_impl.cc

 // Copyright (c) 2012 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 "content/renderer/media/user_media_client_impl.h"
 
 #include <stddef.h>
 
 #include <utility>
 #include <vector>
@@ skipping 1168 matching lines @@
       sources_.erase(it);
       return;
     }
   }
 }
 
 bool UserMediaClientImpl::UserMediaRequestInfo::HasPendingSources() const {
   return !sources_waiting_for_callback_.empty();
 }
 
+void UserMediaClientImpl::OnDestruct() {
+  delete this;
+}
+
 }  // namespace content