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

sdk/lib/_internal/pub_generated/test/dart2js/ignores_non_entrypoint_dart_files_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(
+                'web',
+                [
+                    d.file('file1.dart', 'var main = () => print("hello");'),
+                    d.file('file2.dart', 'void main(arg1, arg2, arg3) => print("hello");'),
+                    d.file('file3.dart', 'class Foo { void main() => print("hello"); }'),
+                    d.file('file4.dart', 'var foo;')])]).create();
+  });
+  integration("build ignores non-entrypoint Dart files", () {
+    schedulePub(
+        args: ["build"],
+        output: new RegExp(r'Built 0 files to "build".'));
+    d.dir(appPath, [d.dir('build', [d.nothing('web')])]).validate();
+  });
+  integration("serve ignores non-entrypoint Dart files", () {
+    pubServe();
+    requestShould404("file1.dart.js");
+    requestShould404("file2.dart.js");
+    requestShould404("file3.dart.js");
+    requestShould404("file4.dart.js");
+    endPubServe();
+  });
+}