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

sdk/lib/_internal/pub_generated/test/global/activate/supports_version_solver_backtracking_test.dart

+import 'package:scheduled_test/scheduled_test.dart';
+import '../../descriptor.dart' as d;
+import '../../test_pub.dart';
+main() {
+  initConfig();
+  integration('performs verison solver backtracking if necessary', () {
+    servePackages((builder) {
+      builder.serve("foo", "1.1.0", pubspec: {
+        "environment": {
+          "sdk": ">=0.1.2 <0.2.0"
+        }
+      });
+      builder.serve("foo", "1.2.0", pubspec: {
+        "environment": {
+          "sdk": ">=0.1.3 <0.2.0"
+        }
+      });
+    });
+    schedulePub(args: ["global", "activate", "foo"]);
+    d.dir(
+        cachePath,
+        [
+            d.dir(
+                'global_packages',
+                [
+                    d.dir('foo', [d.matcherFile('pubspec.lock', contains('1.1.0'))])])]).validate();
+  });
+}