HostResolver: don't interpret NULL callback argument as a request to do synchronous resolution.

net/base/mock_host_resolver.cc

 // Copyright (c) 2011 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 "net/base/mock_host_resolver.h"
 
 #include "base/memory/ref_counted.h"
 #include "base/string_split.h"
 #include "base/string_util.h"
 #include "base/threading/platform_thread.h"
@@ skipping 94 matching lines @@
     int rv = impl_->Resolve(info, addresses, &sync_callback, out_req, net_log);
     if (rv == ERR_IO_PENDING) {
       MessageLoop::ScopedNestableTaskAllower nestable(MessageLoop::current());
       return sync_callback.WaitForResult();
     }
     return rv;
   }
   return impl_->Resolve(info, addresses, callback, out_req, net_log);
 }
 
+int MockHostResolverBase::ResolveFromCache(const RequestInfo& info,
+                                           AddressList* addresses,
+                                           const BoundNetLog& net_log) {
+  return impl_->ResolveFromCache(info, addresses, net_log);
+}
+
 void MockHostResolverBase::CancelRequest(RequestHandle req) {
   impl_->CancelRequest(req);
 }
 
 void MockHostResolverBase::AddObserver(Observer* observer) {
   impl_->AddObserver(observer);
 }
 
 void MockHostResolverBase::RemoveObserver(Observer* observer) {
   impl_->RemoveObserver(observer);
@@ skipping 194 matching lines @@
   CHECK_EQ(old_proc, current_proc_);
 }
 
 void ScopedDefaultHostResolverProc::Init(HostResolverProc* proc) {
   current_proc_ = proc;
   previous_proc_ = HostResolverProc::SetDefault(current_proc_);
   current_proc_->SetLastProc(previous_proc_);
 }
 
 }  // namespace net