arc: Add utility functions to implement ARC content file system

chrome/browser/chromeos/arc/fileapi/intent_helper_util.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 CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_INTENT_HELPER_UTIL_H_
+#define CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_INTENT_HELPER_UTIL_H_
+
+#include "components/arc/common/intent_helper.mojom.h"
+#include "url/gurl.h"
+
+namespace arc {
+namespace intent_helper_util {
+
+// Utility which posts a task to run IntentHelperInstance::GetFileSize.

[hidehiko, 2016/11/10 07:10:10]

Nice. This gets totally clear to me.

+// This function must be called on the IO thread.
+void GetFileSizeOnIOThread(
+    const GURL& arc_url,
+    const mojom::IntentHelperInstance::GetFileSizeCallback& callback);
+
+// Utility which posts a task to run IntentHelperInstance::OpenFileToRead.
+// This function must be called on the IO thread.
+void OpenFileToReadOnIOThread(
+    const GURL& arc_url,
+    const mojom::IntentHelperInstance::OpenFileToReadCallback& callback);
+
+}  // namespace intent_helper_util
+}  // namespace arc
+
+#endif  // CHROME_BROWSER_CHROMEOS_ARC_FILEAPI_INTENT_HELPER_UTIL_H_