Fix crash in DataUrlNavigationBrowserTest.PDF_FormPost_Block with --enable-network-service.

content/browser/loader/navigation_url_loader_network_service.cc

Index: content/browser/loader/navigation_url_loader_network_service.cc
diff --git a/content/browser/loader/navigation_url_loader_network_service.cc b/content/browser/loader/navigation_url_loader_network_service.cc
index 1f7d42831ef96cf2b2f6389fd629c01a6fb39132..5ea32da0135125cc715ca06d52b86eb1e0c89617 100644
--- a/content/browser/loader/navigation_url_loader_network_service.cc
+++ b/content/browser/loader/navigation_url_loader_network_service.cc
@@ -134,7 +134,8 @@ NavigationURLLoaderNetworkService::NavigationURLLoaderNetworkService(
         BrowserThread::IO, FROM_HERE,
         base::Bind(
             &PrepareNavigationOnIOThread, base::Passed(std::move(new_request)),
-            resource_context, resource_type, appcache_handle->core(),
+            resource_context, resource_type,
+            appcache_handle ? appcache_handle->core() : nullptr,
             base::Bind(&NavigationURLLoaderNetworkService::StartURLRequest,
                        weak_factory_.GetWeakPtr())));
     return;