[Presentation API] Use connection proxy to change connection state to 'closed'

third_party/WebKit/public/platform/modules/presentation/WebPresentationConnectionProxy.h

 // Copyright 2017 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.
 
 #ifndef WebPresentationConnectionProxy_h
 #define WebPresentationConnectionProxy_h
 
 namespace blink {
 
 // The implementation the embedder has to provide for the Presentation API to
 // work. This class is used to send messages to a PresentationConnection hosted
 // in a different frame.
 class WebPresentationConnectionProxy {
  public:
   virtual ~WebPresentationConnectionProxy() = default;
+
+  // Close target connection.
+  virtual void close() const = 0;
 };
 
 }  // namespace blink
 
 #endif  // WebPresentationConnectionProxy_h