Implement utility-side host resolver Mojo client.

net/dns/host_resolver_mojo.h

+// Copyright 2015 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.
+
+#ifndef NET_DNS_HOST_RESOLVER_MOJO_H_
+#define NET_DNS_HOST_RESOLVER_MOJO_H_
+
+#include "base/threading/thread_checker.h"
+#include "net/base/address_list.h"

[Anand Mistry (off Chromium), 2015/02/16 06:32:44]

You can forward-declare this one.

[Sam McNally, 2015/02/16 07:24:44]

Done.

+#include "net/dns/host_resolver.h"
+#include "net/interfaces/host_resolver_service.mojom.h"
+
+namespace net {
+
+class BoundNetLog;
+
+class HostResolverMojo : public HostResolver {

[Anand Mistry (off Chromium), 2015/02/16 06:32:44]

Add a short blurb here about what this is.

[Sam McNally, 2015/02/16 07:24:44]

Done.

+ public:
+  HostResolverMojo(interfaces::HostResolverPtr resolver,
+                   mojo::ErrorHandler* error_handler);

[Anand Mistry (off Chromium), 2015/02/16 06:32:44]

I'm having a hard time liking passing in an error handler. I understand why, but
I still don't like it.

A couple of alternate ideas:
- A disconnection callback instead of ErrorHandler.
- Ignore it. If this pipe goes, the browser side will also detect the
disconnection and also kill everything. Also, the proxy connection is likely
dead as well.

[Sam McNally, 2015/02/16 07:24:44]

Switched to a callback. I'd prefer to avoid leaving this in a silently broken
state.

+  ~HostResolverMojo() override;
+
+  // HostResolver overrides.
+  int Resolve(const RequestInfo& info,
+              RequestPriority priority,
+              AddressList* addresses,
+              const CompletionCallback& callback,
+              RequestHandle* request_handle,
+              const BoundNetLog& source_net_log) override;
+  int ResolveFromCache(const RequestInfo& info,
+                       AddressList* addresses,
+                       const BoundNetLog& source_net_log) override;
+  void CancelRequest(RequestHandle req) override;
+
+ private:
+  class Job;
+
+  interfaces::HostResolverPtr resolver_;
+
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(HostResolverMojo);
+};
+
+}  // namespace net
+
+#endif  // NET_DNS_HOST_RESOLVER_MOJO_H_