Factor out snapshot helpers from main.cc.

runtime/bin/BUILD.gn

 # Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 import("gypi_contents.gni")
 import("../runtime_args.gni")
 
 # Generate a resources.cc file for the service isolate without Observatory.
 action("gen_resources_cc") {
   visibility = [ ":*" ]  # Only targets in this file can see this.
@@ skipping 563 matching lines @@
              "$dart_zlib_path",
            ] + extra_deps
 
     defines = extra_defines
 
     if (dart_use_tcmalloc) {
       deps += [ "//third_party/tcmalloc" ]
     }
 
     sources = [
+                "exit.h",
                 "main.cc",
+                "snapshot.cc",
+                "snapshot.h",
                 "vmservice_impl.cc",
                 "vmservice_impl.h",
                 "$target_gen_dir/resources_gen.cc",
               ] + extra_sources
 
     include_dirs = [
       "..",
       "//third_party",
     ]
 
@@ skipping 254 matching lines @@
   ]
   if (is_linux || is_android) {
     cflags = [ "-fPIC" ]
   }
   if (is_win) {
     libs = [ "dart.lib" ]
     abs_root_out_dir = rebase_path(root_out_dir)
     ldflags = [ "/LIBPATH:$abs_root_out_dir" ]
   }
 }