Add a function for usage tracking. It's based on the bug 6426001.

BUG=
TEST=

Review URL: http://codereview.chromium.org/6453001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@76578 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 46 insertions, 0 deletions

diff --git a/webkit/fileapi/file_system_usage_cache.h b/webkit/fileapi/file_system_usage_cache.h
new file mode 100644
index 0000000..32fc9b8
--- /dev/null
+++ b/webkit/fileapi/file_system_usage_cache.h
@@ -0,0 +1,46 @@
+// Copyright (c) 2011 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 WEBKIT_FILEAPI_FILE_SYSTEM_USAGE_CACHE_H_
+#define WEBKIT_FILEAPI_FILE_SYSTEM_USAGE_CACHE_H_
+
+#include "base/basictypes.h"
+#include "base/file_path.h"
+
+namespace fileapi {
+
+class FileSystemUsageCache {
+ public:
+  // Gets the size described in the .usage file.
+  // Returns less than zero if the size is not availble.
+  static int64 GetUsage(const FilePath& usage_file_path);
+
+  // Increments or decrements the "dirty" entry in the .usage file.
+  // Returns false if no .usage is available.
+  static bool IncrementDirty(const FilePath& usage_file_path);
+  static bool DecrementDirty(const FilePath& usage_file_path);
+
+  // Updates the size described in the .usage file.
+  static int UpdateUsage(const FilePath& usage_file_path, int64 fs_usage);
+
+  static bool Exists(const FilePath& usage_file_path);
+  static bool Delete(const FilePath& usage_file_path);
+
+  static const char kUsageFileName[];
+  static const char kUsageFileHeader[];
+  static const int kUsageFileSize;
+  static const int kUsageFileHeaderSize;
+
+ private:
+  // Read the size and the "dirty" entry described in the .usage file.
+  // Returns less than zero if no .usage file is available.
+  static int64 Read(const FilePath& usage_file_path, uint32* dirty);
+
+  static int Write(const FilePath& usage_file_path,
+                   uint32 dirty, int64 fs_usage);
+};
+
+}  // namespace fileapi
+
+#endif  // WEBKIT_FILEAPI_FILE_SYSTEM_USAGE_CACHE_H_