Use realpath() to find the path to the extension unpack dir on posix systems.

base/file_util.h

 // Copyright (c) 2010 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.
 
 // This file contains utility functions for dealing with the local
 // filesystem.
 
 #ifndef BASE_FILE_UTIL_H_
 #define BASE_FILE_UTIL_H_
 
@@ skipping 261 matching lines @@
 
 // Returns the file size. Returns true on success.
 bool GetFileSize(const FilePath& file_path, int64* file_size);
 
 // Returns true if the given path's base name is ".".
 bool IsDot(const FilePath& path);
 
 // Returns true if the given path's base name is "..".
 bool IsDotDot(const FilePath& path);
 
+#if defined(OS_POSIX)
+// Set |real_path| to |path| with symbolic links expanded.
+// Windows support (expanding junctions) comming soon:
+// http://crbug.com/13044
+bool RealPath(const FilePath& path, FilePath* real_path);
+#endif
+
 // Used to hold information about a given file path.  See GetFileInfo below.
 struct FileInfo {
   // The size of the file in bytes.  Undefined when is_directory is true.
   int64 size;
 
   // True if the file corresponds to a directory.
   bool is_directory;
 
   // The last modified time of a file.
   base::Time last_modified;
@@ skipping 277 matching lines @@
 
 #endif  // UNIT_TEST
 
 }  // namespace file_util
 
 // Deprecated functions have been moved to this separate header file,
 // which must be included last after all the above definitions.
 #include "base/file_util_deprecated.h"
 
 #endif  // BASE_FILE_UTIL_H_