[gn] Turn on external_startup_data by default except on ios

BUILD.gn

 # 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.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 import("gni/v8.gni")
 import("//build_overrides/v8.gni")
 
 import("snapshot_toolchain.gni")
 
 declare_args() {
   # Enable the snapshot feature, for fast context creation.
   # http://v8project.blogspot.com/2015/09/custom-startup-snapshots.html
   v8_use_snapshot = true
 
   # Use external files for startup data blobs:
   # the JS builtins sources and the start snapshot.
-  v8_use_external_startup_data = true
+  v8_use_external_startup_data = !is_ios
 
   # Sets -DVERIFY_HEAP.
   v8_enable_verify_heap = false
 
   # Enable compiler warnings when using V8_DEPRECATED apis.
   v8_deprecation_warnings = false
 
   # Enable compiler warnings when using V8_DEPRECATE_SOON apis.
   v8_imminent_deprecation_warnings = false
 
@@ skipping 2191 matching lines @@
   sources = [
     "test/fuzzer/wasm-asmjs.cc",
   ]
 
   deps = [
     ":fuzzer_support",
   ]
 
   configs = [ ":internal_config" ]
 }