Fix http://code.google.com/p/dart/issues/detail?id=15017.

sdk/lib/_internal/compiler/implementation/closure.dart

Index: sdk/lib/_internal/compiler/implementation/closure.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/closure.dart	(revision 30390)
+++ sdk/lib/_internal/compiler/implementation/closure.dart	(working copy)
@@ -92,10 +92,6 @@
 
   bool isInstanceMember() => true;
   bool isAssignable() => false;
-  // The names of closure variables don't need renaming, since their use is very
-  // simple and they have 1-character names in the minified mode.
-  bool hasFixedBackendName() => true;
-  String fixedBackendName() => name;
 
   DartType computeType(Compiler compiler) {
     return variableElement.computeType(compiler);