Revert "Do not use the namer for naming closure elements."

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 83 matching lines @@
  *    (The [getterPrefix] and [setterPrefix] are different in [MinifyNamer]).
  *
  * 3. The `is` and operator uses the following names:
  *
  *        $is<NAME>
  *        $as<NAME>
  *
  * For local variables, the [Namer] only provides *proposed names*. These names
  * must be disambiguated elsewhere.
  */
-class Namer {
+class Namer implements ClosureNamer {
 
   static const List<String> javaScriptKeywords = const <String>[
     // These are current keywords.
     "break", "delete", "function", "return", "typeof", "case", "do", "if",
     "switch", "var", "catch", "else", "in", "this", "void", "continue",
     "false", "instanceof", "throw", "while", "debugger", "finally", "new",
     "true", "with", "default", "for", "null", "try",
 
     // These are future keywords.
     "abstract", "double", "goto", "native", "static", "boolean", "enum",
@@ skipping 850 matching lines @@
   /// If [name] is not an annotated name, the result will not be an annotated
   /// name either.
   String _sanitizeForNatives(String name) {
     if (!name.contains(r'$')) {
       // Prepend $$. The result must not coincide with an annotated name.
       name = '\$\$$name';
     }
     return name;
   }
 
+  /// Generate a unique name for the [id]th closure variable, with proposed name
+  /// [name].
+  ///
+  /// The result is used as the name of [BoxFieldElement]s and
+  /// [ClosureFieldElement]s, and must therefore be unique to avoid breaking an
+  /// invariant in the element model (classes cannot declare multiple fields
+  /// with the same name).
+  ///
+  /// Since the result is used as an element name, it will later show up as a
+  /// *proposed name* when the element is passed to [instanceFieldPropertyName].
+  String getClosureVariableName(String name, int id) {
+    return "${name}_$id";
+  }
+
   /**
    * Returns a proposed name for the given top-level or static element.
    * The returned id is guaranteed to be a valid JS-id.
    */
   String _proposeNameForGlobal(Element element) {
     assert(!element.isInstanceMember);
     String name;
     if (element.isGenerativeConstructor) {
       name = "${element.enclosingClass.name}\$"
              "${element.name}";
@@ skipping 770 matching lines @@
         if (!first) {
           sb.write('_');
         }
         sb.write('_');
         visit(parameter);
         first = true;
       }
     }
   }
 }