Refine the type of a local after it has been used as the receiver of a call.

sdk/lib/_internal/compiler/implementation/closure.dart

 // Copyright (c) 2012, 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.
 
 library closureToClassMapper;
 
 import "elements/elements.dart";
 import "dart2jslib.dart";
 import "dart_types.dart";
 import "scanner/scannerlib.dart" show Token;
@@ skipping 246 matching lines @@
                   this.thisElement)
       : this.freeVariableMapping = new Map<Element, Element>(),
         this.capturedFieldMapping = new Map<Element, Element>(),
         this.capturingScopes = new Map<Node, ClosureScope>(),
         this.usedVariablesInTry = new Set<Element>(),
         this.parametersWithSentinel = new Map<Element, Element>();
 
   bool isClosure() => closureElement != null;
 
   bool isVariableCaptured(Element element) {
-    freeVariableMapping.containsKey(element);
+    return freeVariableMapping.containsKey(element);
   }
 
   bool isVariableBoxed(Element element) {
     Element copy = freeVariableMapping[element];
     return copy != null && !copy.isMember();
   }
 
   void forEachCapturedVariable(void f(Element local, Element field)) {
     freeVariableMapping.forEach((variable, copy) {
       if (variable is BoxElement) return;
@@ skipping 547 matching lines @@
   }
 
   visitTryStatement(TryStatement node) {
     // TODO(ngeoffray): implement finer grain state.
     bool oldInTryStatement = inTryStatement;
     inTryStatement = true;
     node.visitChildren(this);
     inTryStatement = oldInTryStatement;
   }
 }