Infer AsExpression types.

pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart

Index: pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
index 48a7845160516d20b6cb907503d7d3b92afba579..d9eca271cd884e2b49edeb3f498006fef0b6a043 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
@@ -30,8 +30,7 @@ class KernelAsExpression extends AsExpression implements KernelExpression {
   @override
   DartType _inferExpression(
       KernelTypeInferrer inferrer, DartType typeContext, bool typeNeeded) {
-    // TODO(scheglov): implement.
-    return typeNeeded ? const DynamicType() : null;
+    return inferrer.inferAsExpression(typeContext, typeNeeded, operand, type);
   }
 }