Add Transient FileSystem which goes away after its snapsot file is gone

webkit/fileapi/transient_file_util.cc

Index: webkit/fileapi/transient_file_util.cc
diff --git a/webkit/fileapi/transient_file_util.cc b/webkit/fileapi/transient_file_util.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d78ff5e37c8168ee639047277efbcb1c45696e77
--- /dev/null
+++ b/webkit/fileapi/transient_file_util.cc
@@ -0,0 +1,55 @@
+// Copyright (c) 2013 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 "webkit/fileapi/transient_file_util.h"
+
+#include <string>
+
+#include "base/bind.h"
+#include "base/files/file_path.h"
+#include "webkit/fileapi/file_system_operation_context.h"
+#include "webkit/fileapi/file_system_url.h"
+#include "webkit/fileapi/isolated_context.h"
+
+using webkit_blob::ScopedFile;
+
+namespace fileapi {
+
+namespace {
+
+void RevokeFileSystem(const std::string& filesystem_id,
+                      const base::FilePath& /*path*/) {
+  IsolatedContext::GetInstance()->RevokeFileSystem(filesystem_id);
+}
+
+}  // namespace
+
+ScopedFile TransientFileUtil::CreateSnapshotFile(
+    FileSystemOperationContext* context,
+    const FileSystemURL& url,
+    base::PlatformFileError* error,
+    base::PlatformFileInfo* file_info,
+    base::FilePath* platform_path) {
+  DCHECK(file_info);
+  *error = GetFileInfo(context, url, file_info, platform_path);
+  if (*error == base::PLATFORM_FILE_OK && file_info->is_directory)
+    *error = base::PLATFORM_FILE_ERROR_NOT_A_FILE;
+  if (*error != base::PLATFORM_FILE_OK)
+    return ScopedFile();
+
+  // Sets-up a transient filesystem.
+  DCHECK(!platform_path->empty());
+  DCHECK(!url.filesystem_id().empty());
+
+  ScopedFile scoped_file(
+      *platform_path,
+      ScopedFile::DELETE_ON_SCOPE_OUT,
+      context->task_runner());
+  scoped_file.AddScopeOutCallback(
+      base::Bind(&RevokeFileSystem, url.filesystem_id()), NULL);
+
+  return scoped_file.Pass();
+}
+
+}  // namespace fileapi