Return WKNavigation from loadRequest and loadPostRequest.

ios/web/web_state/js/crw_js_post_request_loader.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 IOS_WEB_WEB_STATE_JS_CRW_JS_POST_REQUEST_LOADER_H_
 #define IOS_WEB_WEB_STATE_JS_CRW_JS_POST_REQUEST_LOADER_H_
 
 #import <WebKit/WebKit.h>
 
 @class CRWWKScriptMessageRouter;
 
 // Class to load POST requests in a provided web view via JavaScript.
 @interface CRWJSPOSTRequestLoader : NSObject
 
 // Asynchronously loads a POST |request| in provided |webView|.
 // It temporarily installs JavaScript message routers with |messageRouter| to
 // handle HTTP errors. The |completionHandler| is called once the request has
 // been executed. In case of successful request, the passed error is nil.
 // The |completionHandler| must not be null. The |messageRouter| and |webView|
 // must not be nil. The |request| must be a POST request.
-- (void)loadPOSTRequest:(NSURLRequest*)request
-              inWebView:(WKWebView*)webView
-          messageRouter:(CRWWKScriptMessageRouter*)messageRouter
-      completionHandler:(void (^)(NSError*))completionHandler;
+- (WKNavigation*)loadPOSTRequest:(NSURLRequest*)request
+                       inWebView:(WKWebView*)webView
+                   messageRouter:(CRWWKScriptMessageRouter*)messageRouter
+               completionHandler:(void (^)(NSError*))completionHandler;
 
 @end
 
 #endif  // IOS_WEB_WEB_STATE_JS_CRW_JS_POST_REQUEST_LOADER_H_