Fix a null pointer crasher.

webkit/appcache/appcache_update_job.cc

 // Copyright (c) 2010 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 "webkit/appcache/appcache_update_job.h"
 
 #include "base/compiler_specific.h"
 #include "base/message_loop.h"
 #include "base/string_util.h"
 #include "base/stringprintf.h"
@@ skipping 1162 matching lines @@
   const GURL& url = found->second;
 
   if (!http_info) {
     LoadFromNewestCacheFailed(url, NULL);  // no response found
   } else {
     // Check if response can be re-used according to HTTP caching semantics.
     // Responses with a "vary" header get treated as expired.
     const std::string name = "vary";
     std::string value;
     void* iter = NULL;
-    if (http_info->headers->RequiresValidation(http_info->request_time,
+    if (!http_info->headers ||
+        http_info->headers->RequiresValidation(http_info->request_time,
                                                http_info->response_time,
                                                base::Time::Now()) ||
         http_info->headers->EnumerateHeader(&iter, name, &value)) {
       LoadFromNewestCacheFailed(url, response_info);
     } else {
       DCHECK(group_->newest_complete_cache());
       AppCacheEntry* copy_me = group_->newest_complete_cache()->GetEntry(url);
       DCHECK(copy_me);
       DCHECK(copy_me->response_id() == response_id);
 
@@ skipping 159 matching lines @@
 
   // Break the connection with the group so the group cannot call delete
   // on this object after we've posted a task to delete ourselves.
   group_->SetUpdateStatus(AppCacheGroup::IDLE);
   group_ = NULL;
 
   MessageLoop::current()->DeleteSoon(FROM_HERE, this);
 }
 
 }  // namespace appcache