Infrastructure for reading V8's initial snapshot from external files

gin/v8.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.
 {
   'conditions': [
-    ['OS=="android" or OS=="linux" or OS=="mac" or OS=="win"', {
+    ['v8_use_external_startup_data==1', {
       'variables': {
-        'files': [
-          'test/data/',
+        'isolate_dependency_tracked': [
+          '<(PRODUCT_DIR)/natives_blob.bin',
+          '<(PRODUCT_DIR)/snapshot_blob.bin',
         ],
       },
     }],
   ],
-  'includes': [
-    '../base/base.isolate',
-  ],
 }