Implements ListenForSessionMessages in PresentationServiceImpl; uses Swap to avoid copying large da…

content/renderer/presentation/presentation_dispatcher.cc

 // Copyright 2015 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/presentation/presentation_dispatcher.h"
 
 #include "base/logging.h"
 #include "content/common/presentation/presentation_service.mojom.h"
 #include "content/public/common/service_registry.h"
 #include "content/public/renderer/render_frame.h"
@@ skipping 195 matching lines @@
       base::Unretained(this)));
 
   DCHECK(!session_info.is_null());
   controller_->didChangeSessionState(
       new PresentationSessionClient(session_info.Pass()),
       GetWebPresentationSessionStateFromMojo(session_state));
 }
 
 void PresentationDispatcher::OnSessionMessagesReceived(
     mojo::Array<presentation::SessionMessagePtr> messages) {
-  if (!controller_)
+  // When messages is null, there is an error at presentation service side.
+  if (!controller_ || messages.is_null())
     return;
 
   for (size_t i = 0; i < messages.size(); ++i) {
     if (messages[i]->type ==
         presentation::PresentationMessageType::PRESENTATION_MESSAGE_TYPE_TEXT) {
       controller_->didReceiveSessionTextMessage(
           new PresentationSessionClient(messages[i]->presentation_url,
                                         messages[i]->presentation_id),
           blink::WebString::fromUTF8(messages[i]->message));
     } else {
@@ skipping 21 matching lines @@
   presentation_service_->ListenForSessionStateChange(base::Bind(
       &PresentationDispatcher::OnSessionStateChange,
       base::Unretained(this)));
   presentation_service_->ListenForSessionMessages(
       base::Bind(&PresentationDispatcher::OnSessionMessagesReceived,
       base::Unretained(this)));
   */
 }
 
 }  // namespace content