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

build/shim_headers.gypi

Index: build/shim_headers.gypi
diff --git a/build/shim_headers.gypi b/build/shim_headers.gypi
new file mode 100644
index 0000000000000000000000000000000000000000..56d8d3a719614f086f2097480cebe7c6f9e01539
--- /dev/null
+++ b/build/shim_headers.gypi
@@ -0,0 +1,60 @@
+# Copyright (c) 2012 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 a target to handle shim headers
+# in a consistent manner. To use this the following variables need to be
+# defined:
+#   headers_root_path: string: path to directory containing headers
+#   header_filenames: list: list of header file names
+
+{
+  'variables': {
+    'shim_headers_path': '<(SHARED_INTERMEDIATE_DIR)/shim_headers/<(_target_name)/<(_toolset)',
+    'shim_generator_additional_args%': [],
+  },
+  'include_dirs++': [
+    '<(shim_headers_path)',
+  ],
+  'all_dependent_settings': {
+    # Repeating this with different numbers of plusses is unfortunately required
+    # to make sure that even if this include is inside nested conditions/etc, it
+    # still gets inserted at the beginning of the include_dirs list. See
+    # http://crbug.com/263818 for details.
+    'include_dirs+++': [
+      '<(shim_headers_path)',
+    ],
+    'include_dirs++++': [
+      '<(shim_headers_path)',
+    ],
+    'include_dirs+++++': [
+      '<(shim_headers_path)',
+    ],
+  },
+  'actions': [
+    {
+      'variables': {
+        'generator_path': '<(DEPTH)/tools/generate_shim_headers/generate_shim_headers.py',
+        'generator_args': [
+          '--headers-root', '<(headers_root_path)',
+          '--output-directory', '<(shim_headers_path)',
+          '<@(shim_generator_additional_args)',
+          '<@(header_filenames)',
+        ],
+      },
+      'action_name': 'generate_<(_target_name)_shim_headers',
+      'inputs': [
+        '<(generator_path)',
+      ],
+      'outputs': [
+        '<!@pymod_do_main(generate_shim_headers <@(generator_args) --outputs)',
+      ],
+      'action': ['python',
+                 '<(generator_path)',
+                 '<@(generator_args)',
+                 '--generate',
+      ],
+      'message': 'Generating <(_target_name) shim headers',
+    },
+  ],
+}