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

sdk/lib/_internal/pub_generated/test/serve/gets_first_if_dev_dependency_changed_test.dart

+library pub_tests;
+import 'dart:convert';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+main() {
+  initConfig();
+  integration("gets first if a dev dependency has changed", () {
+    d.dir("foo", [d.libPubspec("foo", "0.0.1"), d.libDir("foo")]).create();
+    d.dir(appPath, [d.pubspec({
+        "name": "myapp",
+        "dev_dependencies": {
+          "foo": {
+            "path": "../foo"
+          }
+        }
+      }), d.file("pubspec.lock", JSON.encode({
+        'packages': {}
+      }))]).create();
+    pubServe(shouldGetFirst: true);
+    requestShouldSucceed("packages/foo/foo.dart", 'main() => "foo";');
+    endPubServe();
+  });
+}