WKNavigation.response is always nil in -[WKNavigationDelegate webView:didReceiveServerRedirectForProvisionalNavigation:]

[Eugene But]

Summary:
The response property of the WKNavigation object passed to -[WKNavigationDelegate webView:didReceiveServerRedirectForProvisionalNavigation:] is always nil. I expected this to be the response that triggered the redirect.

Steps to Reproduce:
1) Create a WKWebView instance and load browsingtest.appspot.com.
2) Click on "redirect301" from the page in the row "Window34".

Sample Code:
- (void)viewDidLoad {
  [super viewDidLoad];
  WKWebViewConfiguration* config = [[WKWebViewConfiguration alloc] init];
  self.webView =
  [[WKWebView alloc] initWithFrame:self.view.bounds configuration:config];
  [self.view addSubview:self.webView];
  self.webView.navigationDelegate = self;
  NSURLRequest* request = [[NSURLRequest alloc]
      initWithURL:[NSURL URLWithString:@"http://browsingtest.appspot.com"]];
  [self.webView loadRequest:request];
  // click redirect301 on the page.
}

- (void)webView:(WKWebView *)webView
didReceiveServerRedirectForProvisionalNavigation:(WKNavigation *)navigation {
  // This should not be nil.
  NSLog(@"%@", navigation.response);
}


Expected Results:
Expected WKNavigation.response to be populated with the response from http://browsingtest.appspot.com/redirect?code=301.


Actual Results:
WKNavigation.response is nil
Hose methods are not implemented:
https://github.com/WebKit/webkit/blob/0190dd5b8c0272beaa705dbc10863a84a3e6af5e/Source/WebKit2/UIProcess/API/Cocoa/WKNavigation.mm

[Eugene But]

Radar ID: 17935346