[Media Gallery] Added code to support mtp device media file system on Windows.

chrome/browser/media_gallery/win/mtp_device_object_enumerator.h

+// Copyright (c) 2012 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.
+//
+// This class enumerates the media transfer protocol (MTP) device objects from
+// a given object entry list.
+
+#ifndef CHROME_BROWSER_MEDIA_GALLERY_WIN_MTP_DEVICE_OBJECT_ENUMERATOR_H_
+#define CHROME_BROWSER_MEDIA_GALLERY_WIN_MTP_DEVICE_OBJECT_ENUMERATOR_H_
+
+#include "base/file_path.h"
+#include "base/threading/thread_checker.h"
+#include "base/time.h"
+#include "chrome/browser/media_gallery/win/mtp_device_object_entry.h"
+#include "webkit/fileapi/file_system_file_util.h"
+
+namespace chrome {
+
+// This class enumerates the media transfer protocol device objects. This class
+// is mainly used to enumerate top-level files of a media device file system.

[Ryan Sleevi, 2013/01/09 00:20:36]

"mainly used"? What other uses does it have? How do those look?

While I'm unfamiliar with the MTP, this code leaves me wondering.

I also tend to make a distinction between how a class should be used / can be
used and how a class is being used. Describing how a class "is being used" is
usually a recipe for comment obsolescence, since it's separated from the code
that's using it. In the long run, it creates more questions than answers.

Describing how a class can or should be used, however, provides much more useful
information to the reader attempting to understand this class.

[kmadhusu, 2013/01/09 18:11:14]

Rephrased the comment.

+// This class supports MTP device file operations. This class is created,
+// destroyed and operated on the blocking pool thread.
+class MTPDeviceObjectEnumerator
+    : public fileapi::FileSystemFileUtil::AbstractFileEnumerator {
+ public:
+  explicit MTPDeviceObjectEnumerator(const MTPDeviceObjectEntries& entries);
+  virtual ~MTPDeviceObjectEnumerator();
+
+  // AbstractFileEnumerator:
+  virtual FilePath Next() OVERRIDE;
+  virtual int64 Size() OVERRIDE;
+  virtual bool IsDirectory() OVERRIDE;
+  virtual base::Time LastModifiedTime() OVERRIDE;
+
+ private:
+  // The directory file object entries.
+  MTPDeviceObjectEntries object_entries_;
+
+  // Iterator to access the individual file object entries.
+  MTPDeviceObjectEntries::const_iterator object_entry_iter_;
+
+  // The current file object entry.
+  MTPDeviceObjectEntry current_object_;
+
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(MTPDeviceObjectEnumerator);
+};
+
+}  // namepsace chrome
+
+#endif  // CHROME_BROWSER_MEDIA_GALLERY_WIN_MTP_DEVICE_OBJECT_ENUMERATOR_H_