Do not use the namer for naming closure elements.

pkg/compiler/lib/src/js_backend/minify_namer.dart

 // Copyright (c) 2011, 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 js_backend;
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  */
 class MinifyNamer extends Namer {
@@ skipping 30 matching lines @@
     if (suggestion != null && !usedNames.contains(suggestion)) {
       freshName = suggestion;
     } else {
       freshName = _getUnusedName(proposedName, usedNames,
           suggestedNames.values);
     }
     usedNames.add(freshName);
     return freshName;
   }
 
-  String getClosureVariableName(String _, int id) {
-    if (id < ALPHABET_CHARACTERS) {
-      return new String.fromCharCodes([_letterNumber(id)]);
-    }
-    // Fall back to a slightly longer name.
-    String basename = _disambiguateMember(null, 'closure');
-    return '${basename}_$id';
-  }
-
   // From issue 7554.  These should not be used on objects (as instance
   // variables) because they clash with names from the DOM. However, it is
   // OK to use them as fields, as we only access fields directly if we know
   // the receiver type.
   static const List<String> _reservedNativeProperties = const <String>[
       'Q', 'a', 'b', 'c', 'd', 'e', 'f', 'r', 'x', 'y', 'z',
       // 2-letter:
       'ch', 'cx', 'cy', 'db', 'dx', 'dy', 'fr', 'fx', 'fy', 'go', 'id', 'k1',
       'k2', 'k3', 'k4', 'r1', 'r2', 'rx', 'ry', 'x1', 'x2', 'y1', 'y2',
       // 3-letter:
@@ skipping 374 matching lines @@
   _BoxFieldNamingScope(Local box, _FieldNamingRegistry registry) :
     super.rootScope(box, registry);
 
   bool containsField(_) => true;
 
   String operator[](Element field) {
     if (!names.containsKey(field)) add(field);
     return names[field];
   }
 }