Migrate ArcBridgeService::Observer and ArcSession::Observer.

components/arc/arc_session_observer.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_ARC_ARC_SESSION_OBSERVER_H_
+#define COMPONENTS_ARC_ARC_SESSION_OBSERVER_H_
+
+#include <ostream>
+
+namespace arc {
+
+// Interface to observe the ARC instance running state.
+class ArcSessionObserver {
+ public:
+  // Describes the reason the ARC instance is stopped.
+  enum class StopReason {
+    // ARC instance has been gracefully shut down.
+    SHUTDOWN,
+
+    // Errors occurred during the ARC instance boot. This includes any failures
+    // before the instance is actually attempted to be started, and also
+    // failures on bootstrapping IPC channels with Android.
+    GENERIC_BOOT_FAILURE,
+
+    // The device is critically low on disk space.
+    LOW_DISK_SPACE,
+
+    // ARC instance has crashed.
+    CRASH,
+  };
+
+  virtual ~ArcSessionObserver() = default;
+
+  // Called when the connection with ARC instance has been established.
+  virtual void OnSessionReady() {}
+
+  // Called when ARC instance is stopped. This is called exactly once
+  // per instance which is Start()ed.
+  virtual void OnSessionStopped(StopReason reason) {}
+};
+
+// Defines "<<" operator for LOGging purpose.
+std::ostream& operator<<(std::ostream& os,
+                         ArcSessionObserver::StopReason reason);
+
+}  // namespace arc
+
+#endif  // COMPONENTS_ARC_ARC_SESSION_OBSERVER_H_