Revert "Reapply r27640: "Emit compile-time error on duplicate parameter names in typedefs.""

sdk/lib/_internal/compiler/implementation/dart_backend/placeholder_collector.dart

 // Copyright (c) 2012, 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 dart_backend;
 
 class LocalPlaceholder {
   final String identifier;
   final Set<Node> nodes;
   LocalPlaceholder(this.identifier) : nodes = new Set<Node>();
@@ skipping 226 matching lines @@
       makeVarDeclarationTypePlaceholder(definitions);
     } else {
       assert(element is ClassElement || element is TypedefElement);
     }
     currentLocalPlaceholders = new Map<String, LocalPlaceholder>();
     compiler.withCurrentElement(element, () {
       elementNode.accept(this);
     });
   }
 
-  // TODO(karlklose): should we create placeholders for these?
-  bool isTypedefParameter(Element element) {
-    return element != null &&
-        element.enclosingElement != null &&
-        element.enclosingElement.isTypedef();
-  }
-
   void tryMakeLocalPlaceholder(Element element, Identifier node) {
     bool isNamedOptionalParameter() {
       FunctionElement function = element.enclosingElement;
       FunctionSignature signature = function.functionSignature;
       if (!signature.optionalParametersAreNamed) return false;
       for (Element parameter in signature.optionalParameters) {
         if (identical(parameter, element)) return true;
       }
       return false;
     }
 
     // TODO(smok): Maybe we should rename privates as well, their privacy
     // should not matter if they are local vars.
     if (node.source.isPrivate()) return;
-    if (element.isParameter() && isNamedOptionalParameter() &&
-        !isTypedefParameter(element)) {
+    if (element.isParameter() && isNamedOptionalParameter()) {
       currentFunctionScope.registerParameter(node);
-    } else if (Elements.isLocal(element) && !isTypedefParameter(element)) {
+    } else if (Elements.isLocal(element)) {
       makeLocalPlaceholder(node);
     }
   }
 
   void tryMakeMemberPlaceholder(Identifier node) {
     assert(node != null);
     if (node.source.isPrivate()) return;
     if (node is Operator) return;
     final identifier = node.source.slowToString();
     if (fixedMemberNames.contains(identifier)) return;
@@ skipping 352 matching lines @@
 
   visitBlock(Block node) {
     for (Node statement in node.statements.nodes) {
       if (statement is VariableDefinitions) {
         makeVarDeclarationTypePlaceholder(statement);
       }
     }
     node.visitChildren(this);
   }
 }