Fix crash when using remote DevTools on CrOS WebUI - check for response_headers

chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.h"
 
 #include <string>
 #include <vector>
 
 #include "base/base64.h"
@@ skipping 644 matching lines @@
   // Ignores x-frame-options for the chrome signin UI.
   const std::string request_spec(
       request->first_party_for_cookies().GetOrigin().spec());
 #if defined(OS_CHROMEOS)
   if (request_spec == chrome::kChromeUIOobeURL ||
       request_spec == chrome::kChromeUIChromeSigninURL) {
 #else
   if (request_spec == chrome::kChromeUIChromeSigninURL) {
 #endif
     net::HttpResponseHeaders* response_headers = request->response_headers();
-    if (response_headers->HasHeader("x-frame-options"))
+    if (response_headers && response_headers->HasHeader("x-frame-options"))
       response_headers->RemoveHeader("x-frame-options");
   }
 
   prerender::URLRequestResponseStarted(request);
 }
 
 void ChromeResourceDispatcherHostDelegate::OnRequestRedirected(
     const GURL& redirect_url,
     net::URLRequest* request,
     content::ResourceContext* resource_context,
@@ skipping 40 matching lines @@
                                        url_request->GetTotalReceivedBytes()));
   }
 }
 
 // static
 void ChromeResourceDispatcherHostDelegate::
     SetExternalProtocolHandlerDelegateForTesting(
     ExternalProtocolHandler::Delegate* delegate) {
   g_external_protocol_handler_delegate = delegate;
 }