Docserver: Fix invalid path usage in CloudStorageFileSystem.

chrome/common/extensions/docs/server2/path_util.py

 # Copyright 2013 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.
 
 import posixpath
 
 
 # TODO(kalman): Write a Path class and use that everywhere rather than a
 # utility class.
 
@@ skipping 11 matching lines @@
   Paths may not start with /, must be posix paths, and for sanity shouldn't
   repeat the path separator //.
   '''
   return not path.startswith('/') and not '\\' in path and not '//' in path
 
 
 def AssertIsValid(path):
   assert IsValid(path), 'Path "%s" is invalid' % path
 
 
+def Join(*paths):
+  assert all(IsValid(path) for path in paths), paths
+  return posixpath.join(*paths)
+
+
 def SplitParent(path):
   '''Returns the parent directory and base name of |path| in a tuple.
   Any trailing slash of |path| is preserved, such that the parent of
   '/hello/world/' is '/hello' and the base is 'world/'.
   '''
   parent, base = posixpath.split(path.rstrip('/'))
   if path.endswith('/'):
     base += '/'
   return parent, base
 
 
 def ToDirectory(path):
   '''Returns a string representing |path| as a directory, that is,
   IsDirectory(result) is True (and does not fail assertions). If |path| is
   already a directory then this is a no-op.
   '''
   return path if IsDirectory(path) else (path + '/')
 
 
 def AssertIsDirectory(path):
   assert IsDirectory(path), '"%s" is not a directory' % path
 
 
 def AssertIsFile(path):
   assert not IsDirectory(path), '"%s" is not a file' % path