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

third_party/WebKit/public/platform/modules/presentation/WebPresentationError.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 WebPresentationError_h
 #define WebPresentationError_h
 
 #include "public/platform/WebString.h"
 
 namespace blink {
 
 struct WebPresentationError {
   enum ErrorType {
     ErrorTypeNoAvailableScreens = 0,
     ErrorTypeSessionRequestCancelled,
     ErrorTypeNoPresentationFound,
     ErrorTypeAvailabilityNotSupported,
+    ErrorTypePreviousStartInProgress,
     ErrorTypeUnknown,
     ErrorTypeLast = ErrorTypeUnknown
   };
 
   WebPresentationError(ErrorType errorType, const WebString& message)
       : errorType(errorType), message(message) {}
 
   ErrorType errorType;
   WebString message;
 };
 
 }  // namespace blink
 
 #endif  // WebPresentationError_h