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

build/mac/asan.gyp

+# Copyright (c) 2013 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.
+
+{
+   'targets': [
+     {
+       'target_name': 'asan_dynamic_runtime',
+       'type': 'none',
+       'variables': {
+         # Every target is going to depend on asan_dynamic_runtime, so allow
+         # this one to depend on itself.
+         'prune_self_dependency': 1,
+         # Path is relative to this GYP file.
+         'asan_rtl_mask_path':
+             '../../third_party/llvm-build/Release+Asserts/lib/clang/*/lib/darwin',
+         'asan_osx_dynamic':
+             '<(asan_rtl_mask_path)/libclang_rt.asan_osx_dynamic.dylib',
+         'asan_iossim_dynamic':
+             '<(asan_rtl_mask_path)/libclang_rt.asan_iossim_dynamic.dylib',
+       },
+       'conditions': [
+         ['OS=="mac"', {
+           'copies': [
+             {
+               'destination': '<(PRODUCT_DIR)',
+               'files': [
+                 '<!(/bin/ls <(asan_osx_dynamic))',
+               ],
+             },
+           ],
+         }],
+         # ASan works with iOS simulator only, not bare-metal iOS.
+         ['OS=="ios" and target_arch=="ia32"', {
+           'toolsets': ['host', 'target'],
+           'copies': [
+             {
+               'destination': '<(PRODUCT_DIR)',
+               'target_conditions': [
+                 ['_toolset=="host"', {
+                   'files': [ '<!(/bin/ls <(asan_osx_dynamic))'],
+                 }],
+                 ['_toolset=="target"', {
+                   'files': [ '<!(/bin/ls <(asan_iossim_dynamic))'],
+                 }],
+               ],
+             },
+           ],
+         }],
+       ],
+     },
+   ],
+}