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

build/common_untrusted.gypi

Index: build/common_untrusted.gypi
diff --git a/build/common_untrusted.gypi b/build/common_untrusted.gypi
new file mode 100644
index 0000000000000000000000000000000000000000..bcc368646bce021fad55a20d5594cb5a993bdda2
--- /dev/null
+++ b/build/common_untrusted.gypi
@@ -0,0 +1,40 @@
+# 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 GYP file should be included for every target in Chromium that is built
+# using the NaCl toolchain.
+{
+  'includes': [
+    '../native_client/build/untrusted.gypi',
+  ],
+  'target_defaults': {
+    'conditions': [
+      # TODO(bradnelson): Drop this once the nacl side does the same.
+      ['target_arch=="x64"', {
+        'variables': {
+          'enable_x86_32': 0,
+        },
+      }],
+      ['target_arch=="ia32" and OS!="win"', {
+        'variables': {
+          'enable_x86_64': 0,
+        },
+      }],
+      ['target_arch=="arm"', {
+        'variables': {
+          'clang': 1,
+        },
+        'defines': [
+          # Needed by build/build_config.h processor architecture detection.
+          '__ARMEL__',
+          # Needed by base/third_party/nspr/prtime.cc.
+          '__arm__',
+          # Disable ValGrind. The assembly code it generates causes the build
+          # to fail.
+          'NVALGRIND',
+        ],
+      }],
+    ],
+  },
+}