Presentation API: Blink changes to allow getAvailability() to be rejected.

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,
         ErrorTypeUnknown,
         ErrorTypeLast = ErrorTypeUnknown
     };
 
     WebPresentationError(ErrorType errorType, const WebString& message)
         : errorType(errorType)
         , message(message)
     {
     }
 
     ErrorType errorType;
     WebString message;
 };
 
 } // namespace blink
 
 #endif // WebPresentationError_h