Adjust return types of spec-mode function expressions to match VM.

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 0e2a3449a75b71259d4f9bd428e5b7c4e939754d..4aab9826dd637415df5913a866d8b2e556b3063c 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
@@ -807,7 +807,7 @@ class KernelFunctionDeclaration extends FunctionDeclaration
   void _inferStatement(KernelTypeInferrer inferrer) {
     inferrer.listener.functionDeclarationEnter(this);
     inferrer.inferLocalFunction(function, null, false, fileOffset,
-        _hasImplicitReturnType ? null : function.returnType, true);
+        _hasImplicitReturnType ? null : function.returnType);
     variable.type = function.functionType;
     inferrer.listener.functionDeclarationExit(this);
   }
@@ -851,7 +851,7 @@ class KernelFunctionExpression extends FunctionExpression
     typeNeeded = inferrer.listener.functionExpressionEnter(this, typeContext) ||
         typeNeeded;
     var inferredType = inferrer.inferLocalFunction(
-        function, typeContext, typeNeeded, fileOffset, null, false);
+        function, typeContext, typeNeeded, fileOffset, null);
     inferrer.listener.functionExpressionExit(this, inferredType);
     return inferredType;
   }