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

gin/gin.gyp

 # Copyright 2013 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': {
     'chromium_code': 1,
     'gin_gen_path': '<(SHARED_INTERMEDIATE_DIR)/gin/',
   },
   'targets': [
@@ skipping 55 matching lines @@
         'public/v8_platform.h',
         'public/wrapper_info.h',
         'runner.cc',
         'runner.h',
         'run_microtasks_observer.cc',
         'run_microtasks_observer.h',
         'shell_runner.cc',
         'shell_runner.h',
         'try_catch.cc',
         'try_catch.h',
+        'v8_initializer.h',
+        'v8_initializer.cc',
         'v8_platform.cc',
         'wrappable.cc',
         'wrappable.h',
         'wrapper_info.cc',
       ],
       'conditions': [
         ['v8_use_external_startup_data==1 and OS=="win"', {
           'dependencies': [
             'gin_v8_snapshot_fingerprint',
             '../crypto/crypto.gyp:crypto',
@@ skipping 76 matching lines @@
         'per_context_data_unittest.cc',
         'shell_runner_unittest.cc',
         'shell/gin_shell_unittest.cc',
         'test/run_all_unittests.cc',
         'test/run_js_tests.cc',
         'wrappable_unittest.cc',
       ],
     },
   ],
 }