Move V8 snapshot loading code from isolate_holder to gin/v8_startup_data.{h,cc}.

gin/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/module_args/v8.gni")
 import("//testing/test.gni")
 
 component("gin") {
   sources = [
     "arguments.cc",
@@ skipping 38 matching lines @@
     "public/v8_platform.h",
     "public/wrapper_info.h",
     "run_microtasks_observer.cc",
     "run_microtasks_observer.h",
     "runner.cc",
     "runner.h",
     "shell_runner.cc",
     "shell_runner.h",
     "try_catch.cc",
     "try_catch.h",
+    "v8_initializer.cc",
+    "v8_initializer.h",
     "v8_platform.cc",
     "wrappable.cc",
     "wrappable.h",
     "wrapper_info.cc",
   ]
 
   defines = [ "GIN_IMPLEMENTATION" ]
 
   public_deps = [
     "//base",
@@ skipping 88 matching lines @@
     "test/run_js_tests.cc",
     "wrappable_unittest.cc",
   ]
 
   deps = [
     ":gin_test",
     "//base/test:test_support",
     "//v8",
   ]
 }