Don't type promote local functions.

pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart

Index: pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart b/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart
index be3152daeccbd69aac8ea8efa5b357c48e85fec3..80229e9c0f6d1324c67e729cacf31626cc8016d6 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart
@@ -198,6 +198,7 @@ abstract class TypePromoterImpl<E, V> extends TypePromoter<E, V> {
   void handleIsCheck(E isExpression, bool isInverted, V variable, DartType type,
       int functionNestingLevel) {
     debugEvent('handleIsCheck');
+    if (!isPromotionCandidate(variable)) return;
     var isCheck = new _IsCheck<V>(
         ++_lastFactSequenceNumber,
         variable,
@@ -212,6 +213,14 @@ abstract class TypePromoterImpl<E, V> extends TypePromoter<E, V> {
     }
   }
 
+  /// Determines whether the given variable should be considered for promotion
+  /// at all.
+  ///
+  /// This is needed because in kernel, [VariableDeclaration] objects are
+  /// sometimes used to represent local functions, which are not subject to
+  /// promotion.
+  bool isPromotionCandidate(V variable);
+
   /// Updates the state to reflect the fact that the given [variable] was
   /// mutated.
   void mutateVariable(V variable, int functionNestingLevel) {