Replaced NavigationContext::IsErrorPage with NavigationContext::GetError

ios/web/public/web_state/navigation_context.h

 // Copyright 2017 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 IOS_WEB_PUBLIC_WEB_STATE_NAVIGATION_CONTEXT_H_
 #define IOS_WEB_PUBLIC_WEB_STATE_NAVIGATION_CONTEXT_H_
 
+#import <Foundation/Foundation.h>
+
 class GURL;
 
 namespace net {
 class HttpResponseHeaders;
 }
 
 namespace web {
 
 class WebState;
 
@@ skipping 10 matching lines @@
   // The URL the WebState is navigating to.
   virtual const GURL& GetUrl() const = 0;
 
   // Whether the navigation happened within the same document. Examples of same
   // document navigations are:
   // * reference fragment navigations
   // * pushState/replaceState
   // * same document history navigation
   virtual bool IsSameDocument() const = 0;
 
-  // Whether the navigation resulted in an error page.
-  virtual bool IsErrorPage() const = 0;
+  // Returns error if the navigation has failed.
+  virtual NSError* GetError() const = 0;
 
   // Returns the response headers for the request, or null if there aren't any
   // response headers or they have not been received yet. The response headers
   // returned should not be modified, as modifications will not be reflected.
   virtual net::HttpResponseHeaders* GetResponseHeaders() const = 0;
 
   virtual ~NavigationContext() {}
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_PUBLIC_WEB_STATE_NAVIGATION_CONTEXT_H_