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

build/android/developer_recommended_flags.gypi

+# Copyright 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.
+
+# This is the set of recommended gyp variable settings for Chrome for Android development.
+#
+# These can be used by copying this file to $CHROME_SRC/chrome/supplement.gypi.
+#
+# Even better, create chrome/supplement.gypi containing the following:
+#   {
+#     'includes': [ '../build/android/developer_recommended_flags.gypi' ]
+#   }
+# and you'll get new settings automatically.
+# When using this method, you can override individual settings by setting them unconditionally (with
+# no %) in chrome/supplement.gypi.
+# I.e. to disable gyp_managed_install but use everything else:
+#   {
+#     'variables': {
+#       'gyp_managed_install': 0,
+#     },
+#     'includes': [ '../build/android/developer_recommended_flags.gypi' ]
+#   }
+
+{
+  'variables': {
+    'variables': {
+      # Set component to 'shared_library' to enable the component build. This builds native code as
+      # many small shared libraries instead of one monolithic library. This slightly reduces the time
+      # required for incremental builds.
+      'component%': 'shared_library',
+    },
+    'component%': '<(component)',
+
+    # When gyp_managed_install is set to 1, building an APK will install that APK on the connected
+    # device(/emulator). To install on multiple devices (or onto a new device), build the APK once
+    # with each device attached. This greatly reduces the time required for incremental builds.
+    #
+    # This comes with some caveats:
+    #   Only works with a single device connected (it will print a warning if
+    #     zero or multiple devices are attached).
+    #   Device must be flashed with a user-debug unsigned Android build.
+    #   Some actions are always run (i.e. ninja will never say "no work to do").
+    'gyp_managed_install%': 1,
+
+    # With gyp_managed_install, we do not necessarily need a standalone APK.
+    # When create_standalone_apk is set to 1, we will build a standalone APK
+    # anyway. For even faster builds, you can set create_standalone_apk to 0.
+    'create_standalone_apk%': 1,
+
+    # Set clang to 1 to use the clang compiler. Clang has much (much, much) better warning/error
+    # messages than gcc.
+    # TODO(cjhopman): Enable this when http://crbug.com/156420 is addressed. Until then, users can
+    # set clang to 1, but Android stack traces will sometimes be incomplete.
+    #'clang%': 1,
+
+    # Set fastbuild to 1 to build with less debugging information. This can greatly decrease linking
+    # time. The downside is that stack traces will be missing useful information (like line
+    # numbers).
+    #'fastbuild%': 1,
+  },
+}