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

build/jar_file_jni_generator.gypi

+# 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 provide a rule
+# to generate jni bindings for system Java-files in a consistent manner.
+#
+# To use this, create a gyp target with the following form:
+# {
+#   'target_name': 'android_jar_jni_headers',
+#   'type': 'none',
+#   'variables': {
+#     'jni_gen_package': 'chrome',
+#     'input_java_class': 'java/io/InputStream.class',
+#   },
+#   'includes': [ '../build/jar_file_jni_generator.gypi' ],
+# },
+#
+# Optional variables:
+#  input_jar_file - The input jar file, if omitted, android_sdk_jar will be used.
+
+{
+  'variables': {
+    'jni_generator': '<(DEPTH)/base/android/jni_generator/jni_generator.py',
+    # A comma separated string of include files.
+    'jni_generator_includes%': (
+        'base/android/jni_generator/jni_generator_helper.h'
+    ),
+    'native_exports%': '--native_exports_optional',
+  },
+  'actions': [
+    {
+      'action_name': 'generate_jni_headers_from_jar_file',
+      'inputs': [
+        '<(jni_generator)',
+        '<(input_jar_file)',
+        '<(android_sdk_jar)',
+      ],
+      'variables': {
+        'java_class_name': '<!(basename <(input_java_class)|sed "s/\.class//")',
+        'input_jar_file%': '<(android_sdk_jar)'
+      },
+      'outputs': [
+        '<(SHARED_INTERMEDIATE_DIR)/<(jni_gen_package)/jni/<(java_class_name)_jni.h',
+      ],
+      'action': [
+        '<(jni_generator)',
+        '-j',
+        '<(input_jar_file)',
+        '--input_file',
+        '<(input_java_class)',
+        '--output_dir',
+        '<(SHARED_INTERMEDIATE_DIR)/<(jni_gen_package)/jni',
+        '--includes',
+        '<(jni_generator_includes)',
+        '--optimize_generation',
+        '<(optimize_jni_generation)',
+        '<(native_exports)',
+      ],
+      'message': 'Generating JNI bindings from  <(input_jar_file)/<(input_java_class)',
+      'process_outputs_as_sources': 1,
+    },
+  ],
+  # This target exports a hard dependency because it generates header
+  # files.
+  'hard_dependency': 1,
+}