Add option to gen_snapshot for creating a Makefile describing a snapshot's dependencies.

runtime/platform/platform_headers.gypi

 # Copyright (c) 2012, 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.
 
 # This file contains headers shared between the vm and bin components.
 {
   'sources': [
     'address_sanitizer.h',
+    'allocation.h',
     'assert.h',
     'c99_support_win.h',
     'floating_point.h',
     'floating_point_win.h',
     'globals.h',
+    'growable_array.h',
     'hashmap.h',
     'inttypes_support_win.h',
     'memory_sanitizer.h',
     'text_buffer.h',
     'utils.h',
   ],
 }