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

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

+import 'package:scheduled_test/scheduled_test.dart';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+const MAIN = """
+import 'dart:async';
+
+import 'a.dart' deferred as a;
+import 'b.dart' deferred as b;
+
+void main() {
+  Future.wait([lazyA.loadLibrary(), lazyB.loadLibrary()]).then((_) {
+    a.fn();
+    b.fn();
+  });
+}
+""";
+const A = """
+library a;
+
+fn() => print("a");
+""";
+const B = """
+library b;
+
+fn() => print("b");
+""";
+main() {
+  initConfig();
+  integration("compiles deferred libraries to separate outputs", () {
+    currentSchedule.timeout *= 3;
+    d.dir(
+        appPath,
+        [
+            d.appPubspec(),
+            d.dir(
+                'web',
+                [
+                    d.file('main.dart', MAIN),
+                    d.file('a.dart', A),
+                    d.file('b.dart', B)])]).create();
+    schedulePub(
+        args: ["build"],
+        output: new RegExp(r'Built 4 files to "build".'));
+    d.dir(
+        appPath,
+        [
+            d.dir(
+                'build',
+                [
+                    d.dir(
+                        'web',
+                        [
+                            d.matcherFile('main.dart.js', isNot(isEmpty)),
+                            d.matcherFile('main.dart.precompiled.js', isNot(isEmpty)),
+                            d.matcherFile('main.dart.js_1.part.js', isNot(isEmpty)),
+                            d.matcherFile('main.dart.js_2.part.js', isNot(isEmpty))])])]).validate();
+  });
+}