Begin the first small step towards using FilePath everywhere:

base/file_path.h

 // Copyright (c) 2008 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.
 
 // FilePath is a container for pathnames stored in a platform's native string
 // type, providing containers for manipulation in according with the
 // platform's conventions for pathnames.  It supports the following path
 // types:
 //
 //                   POSIX            Windows
@@ skipping 127 matching lines @@
   // only to |component| is returned.  |component| must be a relative path;
   // it is an error to pass an absolute path.
   FilePath Append(const StringType& component) const;
 
   // Returns true if this FilePath contains an absolute path.  On Windows, an
   // absolute path begins with either a drive letter specification followed by
   // a separator character, or with two separator characters.  On POSIX
   // platforms, an absolute path begins with a separator character.
   bool IsAbsolute() const;
 
+  // Older Chromium code assumes that paths are always wstrings.
+  // This function converts a wstring to a FilePath, and is useful to smooth
+  // porting that old code to the FilePath API.
+  // It has "Hack" in its name so people feel bad about using it.
+  // TODO(port): remove these functions.
+  static FilePath FromWStringHack(const std::wstring& wstring);
+
+  // Older Chromium code assumes that paths are always wstrings.
+  // This function produces a wstring from a FilePath, and is useful to smooth
+  // porting that old code to the FilePath API.
+  // It has "Hack" in its name so people feel bad about using it.
+  // TODO(port): remove these functions.
+  std::wstring ToWStringHack() const;
+
  private:
   // If this FilePath contains a drive letter specification, returns the
   // position of the last character of the drive letter specification,
   // otherwise returns npos.  This can only be true on Windows, when a pathname
   // begins with a letter followed by a colon.  On other platforms, this always
   // returns npos.
   StringType::size_type FindDriveLetter() const;
 
   // Remove trailing separators from this object.  If the path is absolute, it
   // will never be stripped any more than to refer to the absolute root
   // directory, so "////" will become "/", not "".  A leading pair of
   // separators is never stripped, to support alternate roots.  This is used to
   // support UNC paths on Windows.
   void StripTrailingSeparators();
 
   StringType path_;
 };
 
 // Macros for string literal initialization of FilePath::CharType[].
 #if defined(OS_POSIX)
 #define FILE_PATH_LITERAL(x) x
 #elif defined(OS_WIN)
 #define FILE_PATH_LITERAL(x) L ## x
 #endif  // OS_WIN
 
 #endif  // BASE_FILE_PATH_H_