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

sdk/lib/_internal/pub_generated/test/downgrade/unlock_dependers_test.dart

+library pub_tests;
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+main() {
+  initConfig();
+  integration(
+      "downgrades a locked package's dependers in order to get it to " "min version",
+      () {
+    servePackages((builder) {
+      builder.serve("foo", "2.0.0", deps: {
+        "bar": ">1.0.0"
+      });
+      builder.serve("bar", "2.0.0");
+    });
+    d.appDir({
+      "foo": "any",
+      "bar": "any"
+    }).create();
+    pubGet();
+    d.packagesDir({
+      "foo": "2.0.0",
+      "bar": "2.0.0"
+    }).validate();
+    servePackages((builder) {
+      builder.serve("foo", "1.0.0", deps: {
+        "bar": "any"
+      });
+      builder.serve("bar", "1.0.0");
+    });
+    pubDowngrade(args: ['bar']);
+    d.packagesDir({
+      "foo": "1.0.0",
+      "bar": "1.0.0"
+    }).validate();
+  });
+}