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 container running state.

[Luis Héctor Chávez, 2016/12/13 18:02:54]

This file has "ARC container", "ArcSession", and "ARC instance". Let's
standardize on one. Historically it was "ARC instance", but I'm not opposed to
change to any of the other ones, as long as we're consistent about it.

[hidehiko, 2016/12/14 01:23:32]

Let's use ARC instance, then. According to git grep, it is commonly used.
I'm tempted to use ArcSession, to be consistent with the class name, but IMHO
it's fine at least for now.

+class ArcSessionObserver {
+ public:
+  // Describes the reason the bridge is stopped.

[Luis Héctor Chávez, 2016/12/13 18:02:54]

nit: s/bridge/ARC xxx/ (for whatever xxx we standardize on).

[hidehiko, 2016/12/14 01:23:32]

Done.

+  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 OnReady() {}

[Luis Héctor Chávez, 2016/12/13 18:02:54]

How about OnSessionReady / OnSessionStopped? We use the same pattern with the
InstanceHolder, and it'll avoid naming collisions.

[hidehiko, 2016/12/14 01:23:32]

Done.

+
+  // Called when ARC instance is stopped. This is called exactly once
+  // per instance which is Start()ed.
+  virtual void OnStopped(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_