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

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

+library pub_tests;
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+main() {
+  initConfig();
+  integration(
+      "downgrades one locked hosted package's dependencies if it's " "necessary",
+      () {
+    servePackages((builder) {
+      builder.serve("foo", "2.0.0", deps: {
+        "foo_dep": "any"
+      });
+      builder.serve("foo_dep", "2.0.0");
+    });
+    d.appDir({
+      "foo": "any"
+    }).create();
+    pubGet();
+    d.packagesDir({
+      "foo": "2.0.0",
+      "foo_dep": "2.0.0"
+    }).validate();
+    servePackages((builder) {
+      builder.serve("foo", "1.0.0", deps: {
+        "foo_dep": "<2.0.0"
+      });
+      builder.serve("foo_dep", "1.0.0");
+    });
+    pubDowngrade(args: ['foo']);
+    d.packagesDir({
+      "foo": "1.0.0",
+      "foo_dep": "1.0.0"
+    }).validate();
+  });
+}