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

sdk/lib/_internal/pub_generated/test/get/git/require_pubspec_test.dart

+library pub_tests;
+import '../../descriptor.dart' as d;
+import '../../test_pub.dart';
+main() {
+  initConfig();
+  integration('requires the dependency to have a pubspec', () {
+    ensureGit();
+    d.git('foo.git', [d.libDir('foo')]).create();
+    d.appDir({
+      "foo": {
+        "git": "../foo.git"
+      }
+    }).create();
+    pubGet(
+        error: new RegExp(
+            r'Could not find a file named "pubspec\.yaml" ' r'in "[^\n]*"\.'));
+  });
+}