Fix bot breakage (TBR)

pkg/analyzer/lib/src/cancelable_future.dart

Index: pkg/analyzer/lib/src/cancelable_future.dart
diff --git a/pkg/analyzer/lib/src/cancelable_future.dart b/pkg/analyzer/lib/src/cancelable_future.dart
index 22ce10d71b272a34bd9dcd6b76fd746676ea7521..50b1fa2bf3f3202efd81c0d1416060741a5a9079 100644
--- a/pkg/analyzer/lib/src/cancelable_future.dart
+++ b/pkg/analyzer/lib/src/cancelable_future.dart
@@ -252,7 +252,8 @@ class _CancelableCompleterFuture<T> implements CancelableFuture<T> {
       _completer._outerCompleter.future.catchError(onError, test: test);
 
   @override
-  Future/*<S>*/ then/*<S>*/(FutureOr<S> onValue(T value), {Function onError}) =>
+  Future/*<S>*/ then/*<S>*/(FutureOr/*<S>*/ onValue(T value),
+          {Function onError}) =>
       _completer._outerCompleter.future.then(onValue, onError: onError);
 
   @override
@@ -288,7 +289,8 @@ class _WrappedFuture<T> implements CancelableFuture<T> {
       _future.catchError(onError, test: test);
 
   @override
-  Future/*<S>*/ then/*<S>*/(FutureOr<S> onValue(T value), {Function onError}) =>
+  Future/*<S>*/ then/*<S>*/(FutureOr/*<S>*/ onValue(T value),
+          {Function onError}) =>
       _future.then(onValue, onError: onError);
 
   @override