Stop using third_party\python_26 for many tests.

net/net_unittests.isolate

 # 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.
 {
   'conditions': [
     ['OS=="android" or OS=="linux" or OS=="mac" or OS=="win"', {
       'variables': {
         'isolate_dependency_tracked': [
           '../chrome/test/data/animate1.gif',
           '../chrome/test/data/server-unavailable.html',
@@ skipping 25 matching lines @@
           '<(PRODUCT_DIR)/pyproto/',
           'tools/testserver/',
         ],
       },
     }],
     ['OS=="win"', {
       'variables': {
         'isolate_dependency_tracked': [
           '<(PRODUCT_DIR)/icudt.dll',
         ],
-        'isolate_dependency_untracked': [
-          '../third_party/python_26/',
-        ],
       },
     }],
   ],
 }