[Telemetry] Port page cycler to Telemetry.

tools/telemetry/telemetry/page_set_url_builder.py

 # Copyright (c) 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 os
+import urlparse
 
 # NOTE: This assumes the page_set file uses 'file:///' instead of 'file://',
 # otherwise the '/' will be missing between page_set.base_dir and
 # parsed_url.path.
-def GetUrlBaseDirAndFile(page_set_base_dir, parsed_url):
+def GetUrlBaseDirAndFile(page, page_set_base_dir, parsed_url):
   # Don't use os.path.join otherwise netloc and path can't point to relative
   # directories.
   assert parsed_url.path[0] == '/'
 
   path = (page_set_base_dir +
           parsed_url.netloc +
           parsed_url.path) # pylint: disable=E1101
 
+  if hasattr(page, 'url_base_dir'):
+    parsed_url = urlparse.urlparse(page.url_base_dir)
+    base_path = (page_set_base_dir + parsed_url.netloc + parsed_url.path)
+    return (base_path, path.replace(base_path, ''))
+
   return os.path.split(path)