dart2js: Fix hints in code base.

pkg/compiler/lib/src/js_backend/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.
  *
  * Names are generated through three stages:
@@ skipping 373 matching lines @@
   /// Maps proposed names to *suggested* disambiguated names.
   ///
   /// Suggested names are hints to the [MinifyNamer], suggesting that a specific
   /// names be given to the first item with the given proposed name.
   ///
   /// This is currently used in [MinifyNamer] to assign very short minified
   /// names to things that tend to be used very often.
   final Map<String, String> suggestedGlobalNames = <String, String>{};
   final Map<String, String> suggestedInstanceNames = <String, String>{};
 
-  // All alphanumeric characters.
-  static const String _alphaNumeric =
-      'abcdefghijklmnopqrstuvwxyzABZDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
-
   Namer(Compiler compiler)
       : compiler = compiler,
         constantHasher = new ConstantCanonicalHasher(compiler),
         functionTypeNamer = new FunctionTypeNamer(compiler);
 
   JavaScriptBackend get backend => compiler.backend;
 
   String get deferredTypesName => 'deferredTypes';
   String get isolateName => 'Isolate';
   String get isolatePropertiesName => r'$isolateProperties';
@@ skipping 1387 matching lines @@
         if (!first) {
           sb.write('_');
         }
         sb.write('_');
         visit(parameter);
         first = true;
       }
     }
   }
 }