[PresentationAPI] Added on-session-text-message handler.

Source/modules/presentation/PresentationSession.h

 // Copyright 2014 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 PresentationSession_h
 #define PresentationSession_h
 
 #include "core/events/EventTarget.h"
 #include "core/frame/DOMWindowProperty.h"
 #include "public/platform/modules/presentation/WebPresentationSessionClient.h"
@@ skipping 37 matching lines @@
 
     DEFINE_ATTRIBUTE_EVENT_LISTENER(message);
     DEFINE_ATTRIBUTE_EVENT_LISTENER(statechange);
 
     // Returns true if and only if the WebPresentationSessionClient represents this session.
     bool matches(WebPresentationSessionClient*) const;
 
     // Notifies the session about its state change.
     void didChangeState(WebPresentationSessionState);
 
+    // Notifies the session about new text message.
+    void didReceiveTextMessage(const String& message);
+
 private:
     PresentationSession(LocalFrame*, const String& id, const String& url);
 
     // Returns the |PresentationController| object associated with the frame
     // |Presentation| corresponds to. Can return |nullptr| if the frame is
     // detached from the document.
     PresentationController* presentationController();
 
     // Common send method for both ArrayBufferView and ArrayBuffer.
     void sendInternal(const uint8_t* data, size_t, ExceptionState&);
 
     String m_id;
     String m_url;
     WebPresentationSessionState m_state;
 };
 
 } // namespace blink
 
 #endif // PresentationSession_h