Implement browser-side host resolver Mojo service.

net/dns/mojo_host_resolver_impl.h

Index: net/dns/mojo_host_resolver_impl.h
diff --git a/net/dns/mojo_host_resolver_impl.h b/net/dns/mojo_host_resolver_impl.h
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+++ b/net/dns/mojo_host_resolver_impl.h
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+// 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_MOJO_HOST_RESOLVER_IMPL_H_
+#define NET_DNS_MOJO_HOST_RESOLVER_IMPL_H_
+
+#include <set>
+
+#include "base/macros.h"
+#include "base/threading/thread_checker.h"
+#include "net/interfaces/host_resolver_service.mojom.h"
+
+namespace net {
+
+class HostResolver;
+
+// This is the implementation of the HostResolver Mojo interface.
+// Inbound Mojo requests are sent to the HostResolver passed into the
+// constructor. When destroyed, any outstanding resolver requests are cancelled.
+// If a request's HostResolverRequestClient is shut down, the associated
+// resolver request is cancelled.
+class MojoHostResolverImpl : public interfaces::HostResolver {
+ public:
+  // |resolver| is expected to outlive |this|.
+  explicit MojoHostResolverImpl(net::HostResolver* resolver);
+  ~MojoHostResolverImpl() override;
+
+ private:
+  class Job;
+
+  // Removes |job| from the set of pending jobs, and deletes it.
+  void DeleteJob(Job* job);
+
+  // Overridden from net::interfaces::HostResolver:
+  void Resolve(interfaces::HostResolverRequestInfoPtr request_info,
+               interfaces::HostResolverRequestClientPtr client) override;
+
+  // Resolver for resolving incoming requests. Not owned.
+  net::HostResolver* resolver_;
+
+  // All pending jobs, so they can be cancelled when this service is destroyed.
+  // Owns all jobs.
+  std::set<Job*> pending_jobs_;
+
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(MojoHostResolverImpl);
+};
+
+}  // namespace net
+
+#endif  // NET_DNS_MOJO_HOST_RESOLVER_IMPL_H_