Make requiresContextBox a getter as per Siggi's suggestion.

pkg/compiler/lib/src/ssa/locals_handler.dart

 // Copyright (c) 2016, 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.
 
 import '../closure.dart';
 import '../common.dart';
 import '../elements/elements.dart';
 import '../elements/entities.dart';
 import '../elements/types.dart';
 import '../io/source_information.dart';
@@ skipping 122 matching lines @@
     builder.add(box);
     return box;
   }
 
   /// If the scope (function or loop) [node] has captured variables then this
   /// method creates a box and sets up the redirections.
   void enterScope(ClosureAnalysisInfo closureInfo,
       {bool forGenerativeConstructorBody: false}) {
     // See if any variable in the top-scope of the function is captured. If yes
     // we need to create a box-object.
-    if (!closureInfo.requiresContextBox()) return;
+    if (!closureInfo.requiresContextBox) return;
     HInstruction box;
     // The scope has captured variables.
     if (forGenerativeConstructorBody) {
       // The box is passed as a parameter to a generative
       // constructor body.
       box = builder.addParameter(closureInfo.context, commonMasks.nonNullType);
     } else {
       box = createBox();
     }
     // Add the box to the known locals.
@@ skipping 519 matching lines @@
   final MemberEntity memberContext;
 
   // Avoid slow Object.hashCode.
   final int hashCode = _nextHashCode = (_nextHashCode + 1).toUnsigned(30);
   static int _nextHashCode = 0;
 
   SyntheticLocal(this.name, this.executableContext, this.memberContext);
 
   toString() => 'SyntheticLocal($name)';
 }