Fix cctest + unittest to work with an external snapshot.

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.
 
 # Because standalone V8 builds are not supported, assume this is part of a
 # Chromium build.
 import("//build/module_args/v8.gni")
 
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
@@ skipping 1507 matching lines @@
     direct_dependent_configs = [ ":external_config" ]
   }
 }
 
 if ((current_toolchain == host_toolchain && v8_toolset_for_d8 == "host") ||
     (current_toolchain != host_toolchain && v8_toolset_for_d8 == "target")) {
   executable("d8") {
     sources = [
       "src/d8.cc",
       "src/d8.h",
+      "src/startup-data-util.h",
+      "src/startup-data-util.cc",
     ]
 
     configs -= [ "//build/config/compiler:chromium_code" ]
     configs += [ "//build/config/compiler:no_chromium_code" ]
     configs += [
       ":internal_config",
       ":features",
       ":toolchain",
     ]
 
@@ skipping 16 matching lines @@
       sources += [
         "src/d8-debug.cc",
         "$target_gen_dir/d8-js.cc",
       ]
     }
     if (v8_enable_i18n_support) {
       deps += [ "//third_party/icu" ]
     }
   }
 }