Revert "Delete rtc::Pathname"

This reverts commit 6b9dec0d16f2df59fa2820c5ec1341be52fb9f32.

Reason for revert: speculative revert for breaking internal projects

Original change's description:
> Delete rtc::Pathname
> 
> Bug: webrtc:6424
> Change-Id: Iec01dc5dd1426d4558983b828b67af872107d723
> Reviewed-on: https://webrtc-review.googlesource.com/c/108400
> Commit-Queue: Niels Moller <nisse@webrtc.org>
> Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#25479}

TBR=kwiberg@webrtc.org,nisse@webrtc.org

Change-Id: I3129a81a1d8e36b3e6c67572410bdc478ec4d5e9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:6424
Reviewed-on: https://webrtc-review.googlesource.com/c/109201
Reviewed-by: Qingsi Wang <qingsi@webrtc.org>
Commit-Queue: Qingsi Wang <qingsi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25490}
diff --git a/rtc_base/pathutils.h b/rtc_base/pathutils.h
new file mode 100644
index 0000000..59f2a4a
--- /dev/null
+++ b/rtc_base/pathutils.h
@@ -0,0 +1,79 @@
+/*
+ *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_PATHUTILS_H_
+#define RTC_BASE_PATHUTILS_H_
+
+#include <string>
+
+namespace rtc {
+
+///////////////////////////////////////////////////////////////////////////////
+// Pathname - parsing of pathnames into components, and vice versa.
+//
+// To establish consistent terminology, a filename never contains a folder
+// component.  A folder never contains a filename.  A pathname may include
+// a folder and/or filename component.  Here are some examples:
+//
+//   pathname()      /home/john/example.txt
+//   folder()        /home/john/
+//   filename()                 example.txt
+//   parent_folder() /home/
+//   folder_name()         john/
+//   basename()                 example
+//   extension()                       .txt
+//
+// Basename may begin, end, and/or include periods, but no folder delimiters.
+// If extension exists, it consists of a period followed by zero or more
+// non-period/non-delimiter characters, and basename is non-empty.
+///////////////////////////////////////////////////////////////////////////////
+
+class Pathname {
+ public:
+  // Folder delimiters are slash and backslash
+  static bool IsFolderDelimiter(char ch);
+  static char DefaultFolderDelimiter();
+
+  Pathname();
+  Pathname(const Pathname&);
+  Pathname(Pathname&&);
+  Pathname(const std::string& pathname);
+  Pathname(const std::string& folder, const std::string& filename);
+
+  Pathname& operator=(const Pathname&);
+  Pathname& operator=(Pathname&&);
+
+  // Returns the folder and filename components.  If the pathname is empty,
+  // returns a string representing the current directory (as a relative path,
+  // i.e., ".").
+  std::string pathname() const;
+  void SetPathname(const std::string& pathname);
+  void SetPathname(const std::string& folder, const std::string& filename);
+
+  // SetFolder and AppendFolder will append a folder delimiter, if needed.
+  void SetFolder(const std::string& folder);
+  void AppendFolder(const std::string& folder);
+
+  bool SetBasename(const std::string& basename);
+
+  // SetExtension will prefix a period, if needed.
+  bool SetExtension(const std::string& extension);
+
+  std::string filename() const;
+  bool SetFilename(const std::string& filename);
+
+ private:
+  std::string folder_, basename_, extension_;
+  char folder_delimiter_;
+};
+
+}  // namespace rtc
+
+#endif  // RTC_BASE_PATHUTILS_H_