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

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

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
 ///
 /// Instances of these classes may be created using the factory methods in
 /// `ast_factory.dart`.
@@ skipping 789 matching lines @@
     implements KernelStatement {
   bool _hasImplicitReturnType = false;
 
   KernelFunctionDeclaration(VariableDeclaration variable, FunctionNode function)
       : super(variable, function);
 
   @override
   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);
   }
 
   static void setHasImplicitReturnType(
       KernelFunctionDeclaration declaration, bool hasImplicitReturnType) {
     declaration._hasImplicitReturnType = hasImplicitReturnType;
   }
 }
 
@@ skipping 23 matching lines @@
       collector.recordNotImmediatelyEvident(fileOffset);
     }
   }
 
   @override
   DartType _inferExpression(
       KernelTypeInferrer inferrer, DartType typeContext, bool typeNeeded) {
     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;
   }
 }
 
 /// Concrete shadow object representing an if-null expression.
 ///
 /// An if-null expression of the form `a ?? b` is represented as the kernel
 /// expression:
 ///
@@ skipping 1492 matching lines @@
   }
 
   transformChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 
   visitChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 }