Use the typedef arity to know how to invoke a closure given by the dom.

dart/lib/compiler/implementation/scanner/listener.dart

Index: dart/lib/compiler/implementation/scanner/listener.dart
===================================================================
--- dart/lib/compiler/implementation/scanner/listener.dart	(revision 8049)
+++ dart/lib/compiler/implementation/scanner/listener.dart	(working copy)
@@ -601,8 +601,8 @@
     NodeList typeVariables = popNode(); // TOOD(karlklose): do not throw away.
     Identifier name = popNode();
     TypeAnnotation returnType = popNode();
-    pushElement(new TypedefElement(name.source, compilationUnitElement,
-                                   typedefKeyword));
+    pushElement(new PartialTypedefElement(name.source, compilationUnitElement,
+                                          typedefKeyword));
   }
 
   void handleVoidKeyword(Token token) {
@@ -904,7 +904,7 @@
 
   void endFunctionTypeAlias(Token typedefKeyword, Token endToken) {
     NodeList formals = popNode();
-    NodeList typeParameters = null; // TODO(ahe): Don't discard these.
+    NodeList typeParameters = popNode();
     Identifier name = popNode();
     TypeAnnotation returnType = popNode();
     pushNode(new Typedef(returnType, name, typeParameters, formals,
@@ -1510,6 +1510,25 @@
   Token position() => beginToken; // findMyName doesn't work. I'm nameless.
 }
 
+class PartialTypedefElement extends TypedefElement {
+  final Token token;
+
+  PartialTypedefElement(SourceString name, Element enclosing, this.token)
+      : super(name, enclosing);
+
+  Node parseNode(Compiler compiler) {
+    if (cachedNode !== null) return cachedNode;
+    NodeListener listener = new NodeListener(compiler, enclosingElement);
+    Parser parser = new Parser(listener);
+    Token token = parser.parseTopLevelDeclaration(token);
+    cachedNode = listener.popNode();
+    assert(listener.nodes.isEmpty());
+    return cachedNode;
+  }
+
+  position() => findMyName(token);
+}
+
 Node parse(DiagnosticListener diagnosticListener,
            CompilationUnitElement element,
            doParse(Parser parser)) {