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

sdk/lib/_internal/pub_generated/test/get/path/path_is_file_test.dart

+import 'package:path/path.dart' as path;
+import '../../descriptor.dart' as d;
+import '../../test_pub.dart';
+main() {
+  initConfig();
+  integration('path dependency when path is a file', () {
+    d.dir('foo', [d.libDir('foo'), d.libPubspec('foo', '0.0.1')]).create();
+    d.file('dummy.txt', '').create();
+    var dummyPath = path.join(sandboxDir, 'dummy.txt');
+    d.dir(appPath, [d.appPubspec({
+        "foo": {
+          "path": dummyPath
+        }
+      })]).create();
+    pubGet(
+        error: 'Path dependency for package foo must refer to a '
+            'directory, not a file. Was "$dummyPath".');
+  });
+}