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

chrome/browser/media_gallery/win/recursive_mtp_device_object_enumerator.cc

+// 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.
+//
+// RecursiveMTPDeviceObjectEnumerator implementation.
+
+#include "chrome/browser/media_gallery/win/recursive_mtp_device_object_enumerator.h"
+
+#include "base/file_path.h"
+#include "base/threading/sequenced_worker_pool.h"
+#include "chrome/browser/media_gallery/win/mtp_device_object_entry.h"
+#include "chrome/browser/media_gallery/win/mtp_device_object_enumerator.h"
+#include "chrome/browser/media_gallery/win/mtp_device_operations_util.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace chrome {
+
+RecursiveMTPDeviceObjectEnumerator::RecursiveMTPDeviceObjectEnumerator(
+    IPortableDevice* device,
+    const MTPDeviceObjectEntries& entries)
+    : device_(device),
+      object_entries_(entries),
+      object_entry_iter_(object_entries_.begin()) {
+  DCHECK(content::BrowserThread::GetBlockingPool()->RunsTasksOnCurrentThread());
+  current_enumerator_.reset(new MTPDeviceObjectEnumerator(entries));
+}
+
+RecursiveMTPDeviceObjectEnumerator::~RecursiveMTPDeviceObjectEnumerator() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+}
+
+FilePath RecursiveMTPDeviceObjectEnumerator::Next() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  FilePath path = current_enumerator_->Next();
+  if (!path.empty())
+    return path;
+
+  // We reached the end.
+  if (object_entry_iter_ == object_entries_.end())
+    return FilePath();

[Peter Kasting, 2012/11/01 21:38:37]

Same question as before about whether we're supposed to make the other accessors
return default values once we hit this

[kmadhusu, 2012/11/02 03:27:16]

This function is mainly called from FileUtilHelper class. This is a sample code
from  FileUtilHelper::ReadDirectory.

  while (!(current = file_enum->Next()).empty()) {
    base::FileUtilProxy::Entry entry;
    entry.is_directory = file_enum->IsDirectory();
    entry.name = VirtualPath::BaseName(current).value();
    entry.size = file_enum->Size();
    entry.last_modified_time = file_enum->LastModifiedTime();
    entries->push_back(entry);
  }

You can see that, we query the file properties only when Next() returns an
non-empty file path. So, we don't have to set the default values on other
accessor methods.

+
+  // Enumerate subdirectories of the next media object entry.
+  MTPDeviceObjectEntry next_object_entry = *object_entry_iter_;
+  ++object_entry_iter_;
+
+  MTPDeviceObjectEntries object_entries;
+  bool success = MTPDeviceOperationsUtil::GetDirectoryEntries(
+      device_.get(), next_object_entry.object_id(), &object_entries);
+
+  if (!success || object_entries.empty()) {

[Peter Kasting, 2012/11/01 21:38:37]

Nit: Or just:

  if (!MTPDeviceOperationsUtil::GetDirectoryEntries(
          device_.get(), next_object_entry.object_id(), &object_entries) ||
      object_entries.empty()) {

[kmadhusu, 2012/11/02 03:27:16]

I would like to use the "bool ret = GetFunc()" format.

[Peter Kasting, 2012/11/02 04:08:11]

Again, why?  I may agree with you if you tell me your rationale, but in the
absence of one, longer code + more temps == worse.

[kmadhusu, 2012/11/29 23:58:14]

There is no strong reason. It was easier for me to read. I am fine either way.
Therefore, inlined the function call in the if condition.

+    current_enumerator_.reset(
+        new fileapi::FileSystemFileUtil::EmptyFileEnumerator());
+  } else {
+    current_enumerator_.reset(
+        new MTPDeviceObjectEnumerator(object_entries));
+  }
+  return current_enumerator_->Next();
+}
+
+int64 RecursiveMTPDeviceObjectEnumerator::Size() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  return current_enumerator_->Size();
+}
+
+bool RecursiveMTPDeviceObjectEnumerator::IsDirectory() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  return current_enumerator_->IsDirectory();
+}
+
+base::Time RecursiveMTPDeviceObjectEnumerator::LastModifiedTime() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  return current_enumerator_->LastModifiedTime();
+}
+
+}  // namespace chrome