Add a snapshot of flutter/engine/src/build to our sdk

build/repack_action.gypi

+# 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.
+
+# This file is meant to be included into an action to invoke grit repack in a
+# consistent manner. To use this the following variables need to be
+# defined:
+#   pak_inputs: list: paths of pak files that need to be combined.
+#   pak_output: string: the output pak file path.
+
+{
+  # GYP version: //tools/grit/repack.gni
+  'variables': {
+    'repack_path': '<(DEPTH)/tools/grit/grit/format/repack.py',
+    'repack_options%': [],
+  },
+  'inputs': [
+    '<(repack_path)',
+    '<@(pak_inputs)',
+  ],
+  'outputs': [
+    '<(pak_output)'
+  ],
+  'action': [
+    'python',
+    '<(repack_path)',
+    '<@(repack_options)',
+    '<(pak_output)',
+    '<@(pak_inputs)',
+  ],
+}