[Presentation API] reject request.start() with OperationError instead of UnknownError if previous s…

content/public/common/presentation_session.h

 // 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.
 
 #ifndef CONTENT_PUBLIC_COMMON_PRESENTATION_SESSION_H_
 #define CONTENT_PUBLIC_COMMON_PRESENTATION_SESSION_H_
 
 #include <string>
 
 #include "content/common/content_export.h"
@@ skipping 26 matching lines @@
 
   const GURL presentation_url;
   const std::string presentation_id;
 };
 
 // Possible reasons why an attempt to create a presentation session failed.
 enum PresentationErrorType {
   PRESENTATION_ERROR_NO_AVAILABLE_SCREENS,
   PRESENTATION_ERROR_SESSION_REQUEST_CANCELLED,
   PRESENTATION_ERROR_NO_PRESENTATION_FOUND,
+  PRESENTATION_ERROR_PREVIOUS_START_IN_PROGRESS,
   PRESENTATION_ERROR_UNKNOWN,
 };
 
 // Struct returned when an attempt to create a presentation session failed.
 struct CONTENT_EXPORT PresentationError {
   PresentationError(PresentationErrorType error_type,
                     const std::string& message);
   ~PresentationError();
 
   const PresentationErrorType error_type;
   const std::string message;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_PRESENTATION_SESSION_H_