Refactor serving_dirs.

tools/telemetry/telemetry/page/__init__.py

 # Copyright 2012 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 inspect
 import logging
 import os
 import urlparse
 
 from telemetry import user_story
 from telemetry.page import shared_page_state
@@ skipping 184 matching lines @@
     if self.url.endswith('/'):
       file_path_url += os.sep
     return file_path_url
 
   @property
   def file_path_url_with_scheme(self):
     return 'file://' + self.file_path_url
 
   @property
   def serving_dir(self):
+    if not self.is_file:
+      return None
     file_path = os.path.realpath(self.file_path)
     if os.path.isdir(file_path):
       return file_path
     else:
       return os.path.dirname(file_path)
 
   @property
   def display_name(self):
     if self.name:
       return self.name
     if not self.is_file:
       return self.url
     all_urls = [p.url.rstrip('/') for p in self.page_set if p.is_file]
     common_prefix = os.path.dirname(os.path.commonprefix(all_urls))
     return self.url[len(common_prefix):].strip('/')