Add patch file support to Dart embedder

mojo/dart/embedder/test/BUILD.gn

 # Copyright 2014 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.
 
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//testing/test.gni")
 
 action("generate_test_snapshot_bin") {
   deps = [
     "//dart/runtime/bin:gen_snapshot($host_toolchain)",
@@ skipping 17 matching lines @@
     "//mojo/public/dart/src/struct.dart",
     "//mojo/public/dart/src/stub.dart",
     "//mojo/public/dart/src/timer_queue.dart",
     "//mojo/public/dart/src/types.dart",
   ]
   output = "$target_gen_dir/test_snapshot_gen.bin"
   outputs = [
     output,
   ]
 
-  gen_snapshot_dir = get_label_info(
-      "//dart/runtime/bin:gen_snapshot($host_toolchain)", "root_out_dir")
+  gen_snapshot_dir =
+      get_label_info("//dart/runtime/bin:gen_snapshot($host_toolchain)",
+                     "root_out_dir")
   script = "//dart/runtime/tools/create_snapshot_bin.py"
   builtin_path = rebase_path("//mojo/dart/embedder/builtin.dart")
   bindings_path = rebase_path("//mojo/public/dart/bindings.dart")
   core_path = rebase_path("//mojo/public/dart/core.dart")
   args = [
-    "--executable", rebase_path("$gen_snapshot_dir/gen_snapshot"),
-    "--package_root", rebase_path("$root_gen_dir"),
-    "--script", rebase_path("test_snapshot.dart"),
-    "--output_bin", rebase_path(output, root_build_dir),
-    "--target_os", os,
+    "--executable",
+    rebase_path("$gen_snapshot_dir/gen_snapshot"),
+    "--package_root",
+    rebase_path("$root_gen_dir"),
+    "--script",
+    rebase_path("test_snapshot.dart"),
+    "--output_bin",
+    rebase_path(output, root_build_dir),
+    "--target_os",
+    os,
     "--url_mapping=dart:mojo_bindings,$bindings_path",
     "--url_mapping=dart:mojo_builtin,$builtin_path",
     "--url_mapping=dart:mojo_core,$core_path",
   ]
 }
 
 action("generate_test_snapshot_file") {
   deps = [
     ":generate_test_snapshot_bin",
   ]
   inputs = [
     "//dart/runtime/tools/create_snapshot_file.py",
     "//mojo/dart/embedder/snapshot.cc.tmpl",
     "$target_gen_dir/test_snapshot_gen.bin",
   ]
   output = "$target_gen_dir/test_snapshot.cc"
   outputs = [
     output,
   ]
 
   script = "//dart/runtime/tools/create_snapshot_file.py"
   args = [
-    "--input_bin", rebase_path("$target_gen_dir/test_snapshot_gen.bin"),
-    "--input_cc", rebase_path("//mojo/dart/embedder/snapshot.cc.tmpl"),
-    "--output", rebase_path(output),
+    "--input_bin",
+    rebase_path("$target_gen_dir/test_snapshot_gen.bin"),
+    "--input_cc",
+    rebase_path("//mojo/dart/embedder/snapshot.cc.tmpl"),
+    "--output",
+    rebase_path(output),
   ]
 }
 
 source_set("dart_controller_for_test") {
-  testonly=true
+  testonly = true
   sources = [
     "$target_gen_dir/test_snapshot.cc",
   ]
 
   deps = [
     ":generate_test_snapshot_file",
     "//mojo/dart/embedder:dart_controller_no_snapshot",
   ]
 }
 
 test("dart_unittests") {
   sources = [
     "run_dart_tests.cc",
     "validation_unittest.cc",
   ]
   deps = [
+    ":async_helper",
     ":dart_controller_for_test",
     ":dart_to_cpp_unittests",
     ":expect",
     ":validation_test_input_parser",
     "//base",
     "//crypto:crypto",
     "//mojo/dart/embedder:dart_controller_no_snapshot",
     "//mojo/edk/test:run_all_unittests",
     "//mojo/edk/test:test_support",
     "//mojo/public/cpp/environment",
@@ skipping 15 matching lines @@
 
 copy("validation_test_input_parser") {
   sources = [
     "//mojo/dart/testing/validation_test_input_parser.dart",
   ]
   outputs = [
     "{{source_gen_dir}}/{{source_file_part}}",
   ]
 }
 
+copy("async_helper") {
+  sources = [
+    "//mojo/dart/testing/async_helper.dart",
+  ]
+  outputs = [
+    "{{source_gen_dir}}/{{source_file_part}}",
+  ]
+}
+
 source_set("dart_to_cpp_unittests") {
   testonly = true
   sources = [
     "dart_to_cpp_tests.cc",
   ]
   deps = [
     ":dart_controller_for_test",
     ":dart_to_cpp_bindings",
     "//base",
     "//crypto",
     "//mojo/dart/embedder:dart_controller_no_snapshot",
     "//mojo/edk/test:test_support",
     "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/system",
     "//mojo/public/interfaces/bindings/tests:test_interfaces",
     "//testing/gtest",
   ]
 }
 
 mojom("dart_to_cpp_bindings") {
   sources = [
     "dart_to_cpp.mojom",
   ]
 }