Begin the first small step towards using FilePath everywhere:

base/path_service.h

 // Copyright (c) 2006-2008 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.
 
 #ifndef BASE_PATH_SERVICE_H__
 #define BASE_PATH_SERVICE_H__
 
 #include "build/build_config.h"
 #ifdef OS_WIN
 // TODO(erikkay): this should be removable, but because SetCurrentDirectory
 // is the name of a Windows function, it gets macro-ized to SetCurrentDirectoryW
 // by windows.h, which leads to a different name in the header vs. the impl.
 // Even if we could fix that, it would still hose all callers of the function.
 // The right thing is likely to rename.
 #include <windows.h>
 #endif
 
 #include <string>
 
 #include "base/base_paths.h"
 
+class FilePath;
+
 // The path service is a global table mapping keys to file system paths.  It is
 // OK to use this service from multiple threads.
 //
 class PathService {
  public:
   // Retrieves a path to a special directory or file and places it into the
   // string pointed to by 'path'. If you ask for a directory it is guaranteed
   // to NOT have a path separator at the end. For example, "c:\windows\temp"
   // Directories are also guaranteed to exist when this function succeeds.
   //
   // Returns true if the directory or file was successfully retrieved. On
   // failure, 'path' will not be changed.
+  static bool Get(int key, FilePath* path);
+  // This version, producing a wstring, is deprecated and only kept around
+  // until we can fix all callers.
   static bool Get(int key, std::wstring* path);
 
   // Overrides the path to a special directory or file.  This cannot be used to
   // change the value of DIR_CURRENT, but that should be obvious.  Also, if the
   // path specifies a directory that does not exist, the directory will be
   // created by this method.  This method returns true if successful.
   //
   // If the given path is relative, then it will be resolved against DIR_CURRENT.
   //
   // WARNING: Consumers of PathService::Get may expect paths to be constant
@@ skipping 15 matching lines @@
   // PathService is used, so a the ProviderFunc MUST BE THREADSAFE.
   //
   typedef bool (*ProviderFunc)(int, std::wstring*);
 
   // Call to register a path provider.  You must specify the range "[key_start,
   // key_end)" of supported path keys.
   static void RegisterProvider(ProviderFunc provider,
                                int key_start,
                                int key_end);
  private:
-  static bool GetFromCache(int key, std::wstring* path);
-  static void AddToCache(int key, const std::wstring& path);
+  static bool GetFromCache(int key, FilePath* path);
+  static void AddToCache(int key, const FilePath& path);
   
 };
 
 #endif // BASE_PATH_SERVICE_H__