Convert GeneratedContent to async and use AnalysisDriver for tasks graph.

pkg/analyzer_plugin/tool/spec/check_all_test.dart

Index: pkg/analyzer_plugin/tool/spec/check_all_test.dart
diff --git a/pkg/analyzer_plugin/tool/spec/check_all_test.dart b/pkg/analyzer_plugin/tool/spec/check_all_test.dart
index 150ed8bf6f76edb0730ed522fe64073722987a61..b553b31fa8719cc1eeb691e0765c7bcc0f7052b8 100644
--- a/pkg/analyzer_plugin/tool/spec/check_all_test.dart
+++ b/pkg/analyzer_plugin/tool/spec/check_all_test.dart
@@ -13,11 +13,11 @@ import 'generate_all.dart';
  * Check that all targets have been code generated.  If they haven't tell the
  * user to run generate_all.dart.
  */
-main() {
+main() async {
   String script = Platform.script.toFilePath(windows: Platform.isWindows);
   List<String> components = split(script);
   int index = components.indexOf('analyzer_plugin');
   String pkgPath = joinAll(components.sublist(0, index + 1));
-  GeneratedContent.checkAll(
+  await GeneratedContent.checkAll(
       pkgPath, join('tool', 'spec', 'generate_all.dart'), allTargets);
 }