Remove '<(PRODUCT_DIR)/extensions/' from the dependencies, it doesn't exist anymore.

chrome/unit_tests.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.
 {
   'variables': {
     'isolate_dependency_tracked': [
       '../net/data/ssl/certificates/expired_cert.pem',
       '../net/data/ssl/certificates/test_mail_google_com.pem',
       '../net/data/ssl/certificates/unittest.originbound.der',
       '../net/data/ssl/certificates/unittest.originbound.key.der',
@@ skipping 729 matching lines @@
           '../third_party/python_26/python26.dll',
           '<(PRODUCT_DIR)/icudt.dll',
           'test/data/safe_browsing/download_protection/signed.exe',
           'test/data/safe_browsing/download_protection/unsigned.exe',
           'test/data/safe_browsing/download_protection/wow_helper.exe',
         ],
         'isolate_dependency_untracked': [
           '../ppapi/lib/gl/include/KHR/',
           '../third_party/python_26/Lib/xml/parsers/',
           '../ui/base/glib/',
-          '<(PRODUCT_DIR)/extensions/',
           'test/data/components/flapper/windows/',
         ],
       },
     }, {
       'variables': {
         'isolate_dependency_tracked': [
           '../third_party/tlslite/tlslite/integration/TLSTwistedProtocolWrapper.py',
           'test/data/extensions/unpacker/empty_default_locale.crx',
           'test/data/extensions/unpacker/has_default_missing_locales.crx',
           'test/data/extensions/unpacker/invalid_default_locale.crx',
           'test/data/extensions/unpacker/invalid_messages_file.crx',
           'test/data/extensions/unpacker/missing_default_data.crx',
           'test/data/extensions/unpacker/missing_default_has_locales.crx',
           'test/data/extensions/unpacker/missing_messages_file.crx',
           'test/data/extensions/unpacker/no_locale_data.crx',
         ],
       },
     }],
   ],
 }