Use ArcFileSystemInstance to access files on ARC.

components/arc/test/fake_file_system_instance.cc

+// 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.
+
+#include "components/arc/test/fake_file_system_instance.h"
+
+namespace arc {
+
+FakeFileSystemInstance::FakeFileSystemInstance() = default;
+
+FakeFileSystemInstance::~FakeFileSystemInstance() = default;
+
+void FakeFileSystemInstance::GetFileSize(const std::string& url,
+                                         const GetFileSizeCallback& callback) {}
+
+void FakeFileSystemInstance::OpenFileToRead(
+    const std::string& url,
+    const OpenFileToReadCallback& callback) {}
+
+void FakeFileSystemInstance::RequestMediaScan(
+    const std::vector<std::string>& paths) {}
+
+}  // namespace arc