mediaview: Mount ARC documents provider file system volumes.

components/arc/file_system/arc_file_system_observer.h

+// 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 COMPONENTS_ARC_FILE_SYSTEM_ARC_FILE_SYSTEM_OBSERVER_H_
+#define COMPONENTS_ARC_FILE_SYSTEM_ARC_FILE_SYSTEM_OBSERVER_H_
+
+namespace arc {
+
+class ArcFileSystemObserver {
+ public:
+  virtual ~ArcFileSystemObserver() = default;
+  // Called when ARC file systems are ready.
+  virtual void OnFileSystemsReady() = 0;
+};
+
+}  // namespace arc
+
+#endif  // COMPONENTS_ARC_FILE_SYSTEM_ARC_FILE_SYSTEM_OBSERVER_H_