In strong mode, properly infer the return types of setters as `void`

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

Index: pkg/front_end/lib/src/fasta/kernel/kernel_procedure_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_procedure_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_procedure_builder.dart
index 5b7e77b9106f37b45f173a5ad793c5c19292c14e..8c092c031c11ea22f52c535a8b4d9defd41dc394 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_procedure_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_procedure_builder.dart
@@ -247,11 +247,7 @@ class KernelProcedureBuilder extends KernelFunctionBuilder {
 
   bool get isEligibleForTopLevelInference {
     if (!isInstanceMember) return false;
-    if (returnType == null) {
-      // For now, we skip inferred return types of setters.
-      // TODO(paulberry): fix this.
-      if (!isSetter) return true;
-    }
+    if (returnType == null) return true;
     if (formals != null) {
       for (var formal in formals) {
         if (formal.type == null) return true;