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

build/ios/mac_build.gypi

Index: build/ios/mac_build.gypi
diff --git a/build/ios/mac_build.gypi b/build/ios/mac_build.gypi
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+# 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.
+
+# Xcode throws an error if an iOS target depends on a Mac OS X target. So
+# any place a utility program needs to be build and run, an action is
+# used to run ninja as script to work around this.
+# Example:
+# {
+#   'target_name': 'foo',
+#   'type': 'none',
+#   'variables': {
+#     # The name of a directory used for ninja. This cannot be shared with
+#     # another mac build.
+#     'ninja_output_dir': 'ninja-foo',
+#     # The full path to the location in which the ninja executable should be
+#     # placed. This cannot be shared with another mac build.
+#    'ninja_product_dir':
+#      '<(DEPTH)/xcodebuild/<(ninja_output_dir)/<(CONFIGURATION_NAME)',
+#     # The list of all the gyp files that contain the targets to run.
+#     're_run_targets': [
+#       'foo.gyp',
+#     ],
+#   },
+#   'includes': ['path_to/mac_build.gypi'],
+#   'actions': [
+#     {
+#       'action_name': 'compile foo',
+#       'inputs': [],
+#       'outputs': [],
+#       'action': [
+#         '<@(ninja_cmd)',
+#         # All the targets to build.
+#         'foo1',
+#         'foo2',
+#       ],
+#     },
+#   ],
+# }
+{
+  'variables': {
+    'variables': {
+     'parent_generator%': '<(GENERATOR)',
+    },
+    'parent_generator%': '<(parent_generator)',
+    # Common ninja command line flags.
+    'ninja_cmd': [
+      # Bounce through clean_env to clean up the environment so things
+      # set by the iOS build don't pollute the Mac build.
+      '<(DEPTH)/build/ios/clean_env.py',
+      # ninja must be found in the PATH.
+      'ADD_TO_PATH=<!(echo $PATH)',
+      'ninja',
+      '-C',
+      '<(ninja_product_dir)',
+    ],
+
+    # Common syntax to rerun gyp to generate the Mac projects.
+    're_run_gyp': [
+      'build/gyp_chromium',
+      '--depth=.',
+      # Don't use anything set for the iOS side of things.
+      '--ignore-environment',
+      # Generate for ninja
+      '--format=ninja',
+      # Generate files into xcodebuild/ninja
+      '-Goutput_dir=xcodebuild/<(ninja_output_dir)',
+      # nacl isn't in the iOS checkout, make sure it's turned off
+      '-Ddisable_nacl=1',
+      # Pass through the Mac SDK version.
+      '-Dmac_sdk=<(mac_sdk)',
+      '-Dparent_generator=<(parent_generator)'
+    ],
+
+    # Rerun gyp for each of the projects needed. This is what actually
+    # generates the projects on disk.
+    're_run_gyp_execution':
+      '<!(cd <(DEPTH) && <@(re_run_gyp) <@(re_run_targets))',
+  },
+  # Since these are used to generate things needed by other targets, make
+  # them hard dependencies so they are always built first.
+  'hard_dependency': 1,
+}