dart2js: Fix hints in code base.

pkg/compiler/lib/src/inferrer/map_tracer.dart

 // Copyright (c) 2014, 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.
 
 part of type_graph_inferrer;
 
 Set<String> okMapSelectorsSet = new Set.from(
     const <String>[
       // From Object.
       "==",
@@ skipping 55 matching lines @@
     }
   }
 
   visitDynamicCallSiteTypeInformation(DynamicCallSiteTypeInformation info) {
     super.visitDynamicCallSiteTypeInformation(info);
     Selector selector = info.selector;
     String selectorName = selector.name;
     if (currentUser == info.receiver) {
       if (!okMapSelectorsSet.contains(selectorName)) {
         if (selector.isCall) {
-          int positionalLength = info.arguments.positional.length;
           if (selectorName == 'addAll') {
             // All keys and values from the argument flow into
             // the map.
             TypeInformation map = info.arguments.positional[0];
             if (map is MapTypeInformation) {
               inferrer.analyzeMapAndEnqueue(map);
               mapAssignments.add(map);
             } else {
               // If we could select a component from a [TypeInformation],
               // like the keytype or valuetype in this case, we could
@@ skipping 28 matching lines @@
           return;
         }
       }
     } else if (selector.isCall &&
                !info.targets.every((element) => element.isFunction)) {
       bailout('Passed to a closure');
       return;
     }
   }
 }