Convert GeneratedContent to async and use AnalysisDriver for tasks graph.

pkg/analyzer/tool/summary/check_test.dart

Index: pkg/analyzer/tool/summary/check_test.dart
diff --git a/pkg/analyzer/tool/summary/check_test.dart b/pkg/analyzer/tool/summary/check_test.dart
index baa083ff7e3efbf19ea6775f08d3083e9bb54f64..88d630d0f090935d64108166b8584d0b13b1bd44 100644
--- a/pkg/analyzer/tool/summary/check_test.dart
+++ b/pkg/analyzer/tool/summary/check_test.dart
@@ -15,8 +15,9 @@ import 'generate.dart';
  * Check that the target file has been code generated.  If it hasn't tell the
  * user to run generate.dart.
  */
-main() {
+main() async {
   String script = Platform.script.toFilePath(windows: Platform.isWindows);
   String pkgPath = normalize(join(dirname(script), '..', '..'));
-  GeneratedContent.checkAll(pkgPath, 'tool/summary/generate.dart', allTargets);
+  await GeneratedContent.checkAll(
+      pkgPath, 'tool/summary/generate.dart', allTargets);
 }