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

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

+import 'package:scheduled_test/scheduled_test.dart';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import '../serve/utils.dart';
+main() {
+  initConfig();
+  setUp(() {
+    d.dir(
+        appPath,
+        [
+            d.appPubspec(),
+            d.dir('lib', [d.file('file.dart', 'void main() => print("hello");')]),
+            d.dir('web', [d.file('index.html', 'html')])]).create();
+  });
+  integration("build ignores Dart entrypoints in lib", () {
+    schedulePub(
+        args: ["build", "--all"],
+        output: new RegExp(r'Built 1 file to "build".'));
+    d.dir(appPath, [d.dir('build', [d.nothing('lib')])]).validate();
+  });
+  integration("serve ignores Dart entrypoints in lib", () {
+    pubServe();
+    requestShould404("packages/myapp/main.dart.js");
+    endPubServe();
+  });
+}