Fix declaration of locals in the cps js codegen.

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

 // Copyright (c) 2014, 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.
 
 library code_generator;
 
 import 'glue.dart';
 
 import '../../tree_ir/tree_ir_nodes.dart' as tree_ir;
 import '../../js/js.dart' as js;
@@ skipping 33 matching lines @@
 
   js.Block body;
 
   /// Generates JavaScript code for the body of [function].
   /// The code will be in [body] and the parameters will be in [parameters].
   CodeGenerator(this.glue, this.registry);
 
   void buildFunction(tree_ir.FunctionDefinition function) {
     currentFunction = function.element;
     visitStatement(function.body);
+
+    Set<tree_ir.Variable> parameterSet = new Set<tree_ir.Variable>();
+
     for (tree_ir.Variable parameter in function.parameters) {
       String name = getVariableName(parameter);
       parameters.add(new js.Parameter(name));
+      parameterSet.add(parameter);
     }
 
     List<js.VariableInitialization> jsVariables = <js.VariableInitialization>[];
 
     for (tree_ir.Variable variable in variableNames.keys) {
+      if (parameterSet.contains(variable)) continue;
       String name = getVariableName(variable);
       js.VariableInitialization jsVariable = new js.VariableInitialization(
         new js.VariableDeclaration(name),
         null);
       jsVariables.add(jsVariable);
     }
 
     if (jsVariables.length > 0) {
       // Would be nice to avoid inserting at the beginning of list.
       accumulator.insert(0, new js.ExpressionStatement(
@@ skipping 211 matching lines @@
   @override
   void visitReturn(tree_ir.Return node) {
     if (node.value != null) {
       accumulator.add(new js.Return(visitExpression(node.value)));
     }
   }
 
   bool isNullLiteral(js.Expression exp) => exp is js.LiteralNull;
 
 }