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

sdk/lib/_internal/pub_generated/test/real_version_test.dart

+library pub_tests;
+import 'dart:io';
+import 'package:path/path.dart' as path;
+import 'package:scheduled_test/scheduled_process.dart';
+import 'package:scheduled_test/scheduled_test.dart';
+import '../lib/src/exit_codes.dart' as exit_codes;
+import '../lib/src/sdk.dart' as sdk;
+import 'test_pub.dart';
+main() {
+  initConfig();
+  integration('parse the real SDK "version" file', () {
+    var pubPath = path.join(
+        sdk.rootDirectory,
+        'bin',
+        Platform.operatingSystem == "windows" ? "pub.bat" : "pub");
+    var pub = new ScheduledProcess.start(pubPath, ['version']);
+    pub.stdout.expect(startsWith("Pub"));
+    pub.shouldExit(exit_codes.SUCCESS);
+  });
+}