Add a Dns preresolve interface in //content

net/dns/single_request_host_resolver.cc

Index: net/dns/single_request_host_resolver.cc
diff --git a/net/dns/single_request_host_resolver.cc b/net/dns/single_request_host_resolver.cc
index 7974abafeef3518983a1d4604e3f5382c6f6d96c..2b05629b53135d93f2671541e3008d17839d6629 100644
--- a/net/dns/single_request_host_resolver.cc
+++ b/net/dns/single_request_host_resolver.cc
@@ -8,6 +8,8 @@
 #include "base/bind_helpers.h"
 #include "base/compiler_specific.h"
 #include "base/logging.h"
+#include "base/memory/ptr_util.h"
+#include "net/base/address_list.h"
 #include "net/base/net_errors.h"
 
 namespace net {
@@ -15,9 +17,9 @@ namespace net {
 SingleRequestHostResolver::SingleRequestHostResolver(HostResolver* resolver)
     : resolver_(resolver),
       cur_request_(NULL),
-      callback_(
-          base::Bind(&SingleRequestHostResolver::OnResolveCompletion,
-                     base::Unretained(this))) {
+      callback_(base::Bind(&SingleRequestHostResolver::OnResolveCompletion,
+                           base::Unretained(this))),
+      default_addresses_(nullptr) {
   DCHECK(resolver_ != NULL);
 }
 
@@ -30,10 +32,14 @@ int SingleRequestHostResolver::Resolve(const HostResolver::RequestInfo& info,
                                        AddressList* addresses,
                                        const CompletionCallback& callback,
                                        const BoundNetLog& net_log) {
-  DCHECK(addresses);
   DCHECK_EQ(false, callback.is_null());
   DCHECK(cur_request_callback_.is_null()) << "resolver already in use";
 
+  if (!addresses) {
+    default_addresses_ = base::WrapUnique(new AddressList);
+    addresses = default_addresses_.get();
+  }
+
   HostResolver::RequestHandle request = NULL;
 
   // We need to be notified of completion before |callback| is called, so that