Add Future.timeout.

sdk/lib/_internal/pub/lib/src/error_group.dart

Index: sdk/lib/_internal/pub/lib/src/error_group.dart
diff --git a/sdk/lib/_internal/pub/lib/src/error_group.dart b/sdk/lib/_internal/pub/lib/src/error_group.dart
index ea924e83e2f734d3b5c30a5d18010a1cb45ac2f1..ae0410f21c742192def5246849a01882187bd303 100644
--- a/sdk/lib/_internal/pub/lib/src/error_group.dart
+++ b/sdk/lib/_internal/pub/lib/src/error_group.dart
@@ -194,6 +194,11 @@ class _ErrorGroupFuture implements Future {
     return _completer.future.whenComplete(action);
   }
 
+  Future timeout(Duration timeLimit, [void onTimeout()]) {
+    _hasListeners = true;
+    return _completer.future.timeout(timeLimit, onTimeout);
+  }
+
   Stream asStream() {
     _hasListeners = true;
     return _completer.future.asStream();