Fail if an isolate entry refers to a missing file.

mojo/mojo_apps_js_unittests.isolate

 # Copyright 2014 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.
 {
   'includes': [
     '../third_party/icu/icu.isolate',
   ],
   'conditions': [
     ['OS=="win" or OS=="mac" or OS=="linux"', {
       'variables': {
@@ skipping 12 matching lines @@
           '<(PRODUCT_DIR)/gen/mojo/public/interfaces/bindings/tests/',
           'apps/js/',
           'bindings/js/',
           'public/js/bindings/',
         ],
       },
     }],
     ['OS=="win"', {
       'variables': {
         'isolate_dependency_tracked': [
-          '<(PRODUCT_DIR)/mojo_system.dll',
           '<(PRODUCT_DIR)/mojo_test_support.dll',
         ],
       },
     }],
     ['OS=="linux"', {
       'variables': {
         'isolate_dependency_tracked': [
           '<(PRODUCT_DIR)/lib/libmojo_test_support.so',
         ],
       },
     }],
     ['OS=="mac"', {
       'variables': {
         'isolate_dependency_tracked': [
           '<(PRODUCT_DIR)/libmojo_test_support.dylib',
         ],
       },
     }],
   ],
 }