Await in DefaultFixContributor.internalComputeFixes() to catch exceptions.

pkg/analysis_server/lib/src/services/correction/fix_internal.dart

Index: pkg/analysis_server/lib/src/services/correction/fix_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
index 7f7f986e84c6d567fdf08e82e60b131ee0b0109a..9c19900a1d90f438e6406a8226d635e2ce24c6e2 100644
--- a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
@@ -78,7 +78,8 @@ class DefaultFixContributor extends DartFixContributor {
   Future<List<Fix>> internalComputeFixes(DartFixContext context) async {
     try {
       FixProcessor processor = new FixProcessor(context);
-      return processor.compute();
+      List<Fix> fixes = await processor.compute();
+      return fixes;
     } on CancelCorrectionException {
       return Fix.EMPTY_LIST;
     }