Store the async-await compiled pub code directly in the repo.

sdk/lib/_internal/pub_generated/test/dart2js/includes_source_maps_in_debug_test.dart

+import 'package:scheduled_test/scheduled_test.dart';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+main() {
+  initConfig();
+  integration("includes source map URLs in a debug build", () {
+    d.dir(
+        appPath,
+        [
+            d.appPubspec(),
+            d.dir(
+                "web",
+                [d.file("main.dart", "void main() => print('hello');")])]).create();
+    schedulePub(
+        args: ["build", "--mode", "debug"],
+        output: new RegExp(r'Built \d+ files to "build".'),
+        exitCode: 0);
+    d.dir(
+        appPath,
+        [
+            d.dir(
+                'build',
+                [
+                    d.dir(
+                        'web',
+                        [
+                            d.matcherFile('main.dart.js', contains("# sourceMappingURL=main.dart.js.map")),
+                            d.matcherFile(
+                                'main.dart.js.map',
+                                contains('"file": "main.dart.js"'))])])]).validate();
+  });
+}