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

sdk/lib/_internal/compiler/implementation/resolution/members.dart

Index: sdk/lib/_internal/compiler/implementation/resolution/members.dart
diff --git a/sdk/lib/_internal/compiler/implementation/resolution/members.dart b/sdk/lib/_internal/compiler/implementation/resolution/members.dart
index b9deb490f1b85dc001938f92274757a6a2ad2dc7..73723474460c678b4201df23a7e66c5a560e262f 100644
--- a/sdk/lib/_internal/compiler/implementation/resolution/members.dart
+++ b/sdk/lib/_internal/compiler/implementation/resolution/members.dart
@@ -1723,30 +1723,6 @@ abstract class MappingVisitor<T> extends CommonResolverVisitor<T> {
     }
     return type;
   }
-
-  Element defineElement(Node node, Element element,
-                        {bool doAddToScope: true}) {
-    compiler.ensure(element != null);
-    mapping[node] = element;
-    if (doAddToScope) {
-      Element existing = scope.add(element);
-      if (existing != element) {
-        reportDuplicateDefinition(node, element, existing);
-      }
-    }
-    return element;
-  }
-
-  void reportDuplicateDefinition(name, Spannable definition,
-                                 Spannable existing) {
-    compiler.reportError(
-        definition,
-        MessageKind.DUPLICATE_DEFINITION, {'name': name});
-    compiler.reportMessage(
-        compiler.spanFromSpannable(existing),
-        MessageKind.EXISTING_DEFINITION.error({'name': name}),
-        Diagnostic.INFO);
-  }
 }
 
 /**
@@ -1939,6 +1915,24 @@ class ResolverVisitor extends MappingVisitor<Element> {
     return null;
   }
 
+  Element defineElement(Node node, Element element,
+                        {bool doAddToScope: true}) {
+    compiler.ensure(element != null);
+    mapping[node] = element;
+    if (doAddToScope) {
+      Element existing = scope.add(element);
+      if (existing != element) {
+        compiler.reportError(
+            node, MessageKind.DUPLICATE_DEFINITION, {'name': node});
+        compiler.reportMessage(
+            compiler.spanFromSpannable(existing),
+            MessageKind.EXISTING_DEFINITION.error({'name': node}),
+            Diagnostic.INFO);
+      }
+    }
+    return element;
+  }
+
   bool isNamedConstructor(Send node) => node.receiver != null;
 
   Selector getRedirectingThisOrSuperConstructorSelector(Send node) {
@@ -2316,10 +2310,14 @@ class ResolverVisitor extends MappingVisitor<Element> {
       if (namedArgument != null) {
         SourceString source = namedArgument.name.source;
         if (seenNamedArguments.containsKey(source)) {
-          reportDuplicateDefinition(
-              source,
+          compiler.reportError(
               argument,
-              seenNamedArguments[source]);
+              MessageKind.DUPLICATE_DEFINITION,
+              {'name': source});
+          compiler.reportMessage(
+              compiler.spanFromSpannable(seenNamedArguments[source]),
+              MessageKind.EXISTING_DEFINITION.error({'name': source}),
+              Diagnostic.INFO);
         } else {
           seenNamedArguments[source] = namedArgument;
         }
@@ -3337,16 +3335,12 @@ class TypedefResolverVisitor extends TypeDefinitionVisitor {
     scope = new TypeDeclarationScope(scope, element);
     resolveTypeVariableBounds(node.typeParameters);
 
-    FunctionSignature signature = SignatureResolver.analyze(
+    element.functionSignature = SignatureResolver.analyze(
         compiler, node.formals, node.returnType, element,
         defaultValuesAllowed: false);
 
-    scope = new MethodScope(scope, element);
-    signature.forEachParameter((Element element) {
-      defineElement(element.parseNode(compiler), element);
-    });
-
-    element.alias = compiler.computeFunctionType(element, signature);
+    element.alias = compiler.computeFunctionType(
+        element, element.functionSignature);
 
     void checkCyclicReference() {
       var visitor = new TypedefCyclicVisitor(compiler, element);