[Sync] Implements the loopback sync server.

components/sync/engine_impl/loopback_server/loopback_connection_manager.h

+// Copyright 2016 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 COMPONENTS_SYNC_ENGINE_IMPL_LOOPBACK_SERVER_LOOPBACK_CONNECTION_MANAGER_H_
+#define COMPONENTS_SYNC_ENGINE_IMPL_LOOPBACK_SERVER_LOOPBACK_CONNECTION_MANAGER_H_
+
+#include <string>
+
+#include "components/sync/engine_impl/loopback_server/loopback_server.h"
+#include "components/sync/engine_impl/net/server_connection_manager.h"
+
+namespace syncer {
+
+// This class implements the ServerConnectionManager interface for a local
+// in-memory virtual connection to the LoopbackServer. Since there is no network
+// connection to be established we only have to handle POSTs and they will
+// always succeed.
+class LoopbackConnectionManager : public ServerConnectionManager {

[pavely, 2016/10/06 23:48:45]

In today's code we don't have a way to inject server connection manager.
Specific implementation of it is instantiated in SyncManagerImpl::Init. Fake
server injects itself through NetworkResources, which is a bit more work.

[pastarmovj, 2016/10/13 14:13:39]

I was planning on conditionally creating one or the other in the Init function.
See my proof of concept here https://codereview.chromium.org/2106743002/ . Of
course I am going to follow your wisdom on this front, I just wanted to show you
what my solution was.

+ public:
+  LoopbackConnectionManager(CancelationSignal* signal,
+                            const base::FilePath& persistent_file);
+  ~LoopbackConnectionManager() override;
+
+ private:
+  // Overridden ServerConnectionManager functions.
+  bool PostBufferToPath(PostBufferParams* params,
+                        const std::string& path,
+                        const std::string& auth_token) override;
+
+  // The loopback server that will handle the requests locally.
+  LoopbackServer loopback_server_;
+
+  DISALLOW_COPY_AND_ASSIGN(LoopbackConnectionManager);
+};
+
+}  // namespace syncer
+
+#endif  // COMPONENTS_SYNC_ENGINE_IMPL_LOOPBACK_SERVER_LOOPBACK_CONNECTION_MANAGER_H_