Fix hints reported by analyzer.

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.namer;
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  */
 class MinifyNamer extends Namer
@@ skipping 299 matching lines @@
 ///
 /// This class implements a naming scheme by counting the distance from
 /// a given constructor to [Object], where distance is the number of
 /// constructors declared along the inheritance chain.
 class _ConstructorBodyNamingScope {
   final int _startIndex;
   final List _constructors;
 
   int get numberOfConstructors => _constructors.length;
 
-  _ConstructorBodyNamingScope _superScope;
-
   _ConstructorBodyNamingScope.rootScope(ClassElement cls)
-      : _superScope = null,
-        _startIndex = 0,
+      : _startIndex = 0,
         _constructors = cls.constructors.toList(growable: false);
 
   _ConstructorBodyNamingScope.forClass(
       ClassElement cls, _ConstructorBodyNamingScope superScope)
-      : _superScope = superScope,
-        _startIndex = superScope._startIndex + superScope.numberOfConstructors,
+      : _startIndex = superScope._startIndex + superScope.numberOfConstructors,
         _constructors = cls.constructors.toList(growable: false);
 
   // Mixin Applications have constructors but we never generate code for them,
   // so they do not count in the inheritance chain.
   _ConstructorBodyNamingScope.forMixinApplication(
       ClassElement cls, _ConstructorBodyNamingScope superScope)
-      : _superScope = superScope,
-        _startIndex = superScope._startIndex + superScope.numberOfConstructors,
+      : _startIndex = superScope._startIndex + superScope.numberOfConstructors,
         _constructors = const [];
 
   factory _ConstructorBodyNamingScope(ClassElement cls,
       Map<ClassElement, _ConstructorBodyNamingScope> registry) {
     return registry.putIfAbsent(cls, () {
       if (cls.superclass == null) {
         return new _ConstructorBodyNamingScope.rootScope(cls);
       } else if (cls.isMixinApplication) {
         return new _ConstructorBodyNamingScope.forMixinApplication(
             cls, new _ConstructorBodyNamingScope(cls.superclass, registry));
@@ skipping 37 matching lines @@
     String prefix =
         selector.isGetter ? r"$get" : selector.isSetter ? r"$set" : "";
     String callSuffix = selector.isCall
         ? callSuffixForStructure(selector.callStructure).join()
         : "";
     String suffix = suffixForGetInterceptor(classes);
     String fullName = "\$intercepted$prefix\$$root$callSuffix\$$suffix";
     return _disambiguateInternalGlobal(fullName);
   }
 }