[Presentation API] check if frame() is null before accessing presentation.receiver attr

third_party/WebKit/Source/modules/presentation/Presentation.cpp

 // 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.
 
 #include "modules/presentation/Presentation.h"
 
 #include "core/dom/Document.h"
 #include "core/frame/LocalFrame.h"
 #include "modules/presentation/PresentationController.h"
 #include "modules/presentation/PresentationReceiver.h"
@@ skipping 30 matching lines @@
   if (!frame())
     return;
 
   PresentationController* controller = PresentationController::from(*frame());
   if (!controller)
     return;
   controller->setDefaultRequestUrl(request ? request->url() : KURL());
 }
 
 PresentationReceiver* Presentation::receiver() {
-  PresentationController* controller = PresentationController::from(*frame());
-  auto* client = controller ? controller->client() : nullptr;
+  if (!frame())
+    return nullptr;
   // TODO(crbug.com/647296): only return something if the Blink instance is
   // running in presentation receiver mode. The flag PresentationReceiver could
   // be used for that.
-  if (!m_receiver)
+  if (!m_receiver) {
+    PresentationController* controller = PresentationController::from(*frame());
+    auto* client = controller ? controller->client() : nullptr;
     m_receiver = new PresentationReceiver(frame(), client);
+  }
   return m_receiver;
 }
 
 }  // namespace blink