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

Source/modules/presentation/PresentationSession.cpp

Index: Source/modules/presentation/PresentationSession.cpp
diff --git a/Source/modules/presentation/PresentationSession.cpp b/Source/modules/presentation/PresentationSession.cpp
index b4a0ec9be96c6242083d4520e4ecc7d6442b1c0b..6c6e9380d43916753372d614e9046f7806214c83 100644
--- a/Source/modules/presentation/PresentationSession.cpp
+++ b/Source/modules/presentation/PresentationSession.cpp
@@ -10,6 +10,7 @@
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/events/Event.h"
+#include "core/events/MessageEvent.h"
 #include "core/frame/LocalFrame.h"
 #include "modules/EventTargetModules.h"
 #include "modules/presentation/Presentation.h"
@@ -135,6 +136,11 @@ void PresentationSession::sendInternal(const uint8_t* data, size_t size, Excepti
         controller->send(m_url, m_id, data, size);
 }
 
+void PresentationSession::didReceiveTextMessage(const String& message)
+{
+    dispatchEvent(MessageEvent::create(message));
+}
+
 void PresentationSession::close()
 {
     if (m_state != WebPresentationSessionState::Connected)