Introduce Identity Service and its initial usage

services/identity/identity_service.h

Index: services/identity/identity_service.h
diff --git a/services/identity/identity_service.h b/services/identity/identity_service.h
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+++ b/services/identity/identity_service.h
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+// Copyright 2017 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 SERVICES_IDENTITY_IDENTITY_SERVICE_H_
+#define SERVICES_IDENTITY_IDENTITY_SERVICE_H_
+
+#include "services/identity/public/interfaces/identity_manager.mojom.h"
+#include "services/service_manager/public/cpp/interface_factory.h"
+#include "services/service_manager/public/cpp/service.h"
+
+class SigninManagerBase;
+
+namespace identity {
+
+class IdentityService
+    : public service_manager::Service,
+      public service_manager::InterfaceFactory<mojom::IdentityManager> {
+ public:
+  IdentityService(SigninManagerBase* signin_manager);
+  ~IdentityService() override;
+
+ private:
+  // |Service| override:
+  void OnStart() override;
+  bool OnConnect(const service_manager::ServiceInfo& remote_info,
+                 service_manager::InterfaceRegistry* registry) override;
+
+  // InterfaceFactory<mojom::IdentityManager>:
+  void Create(const service_manager::Identity& remote_identity,
+              mojom::IdentityManagerRequest request) override;
+
+  SigninManagerBase* signin_manager_;
+
+  DISALLOW_COPY_AND_ASSIGN(IdentityService);
+};
+
+}  // namespace identity
+
+#endif  // SERVICES_IDENTITY_IDENTITY_SERVICE_H_