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

dart/lib/compiler/implementation/resolver.dart

Index: dart/lib/compiler/implementation/resolver.dart
===================================================================
--- dart/lib/compiler/implementation/resolver.dart	(revision 8049)
+++ dart/lib/compiler/implementation/resolver.dart	(working copy)
@@ -237,6 +237,10 @@
     return measure(() => SignatureResolver.analyze(compiler, element));
   }
 
+  FunctionSignature resolveTypedef(TypedefElement element) {
+    return measure(() => SignatureResolver.analyzeTypedef(compiler, element));
+  }
+
   error(Node node, MessageKind kind, [arguments = const []]) {
     ResolutionError message = new ResolutionError(kind, arguments);
     compiler.reportError(node, message);
@@ -1130,12 +1134,7 @@
           type = new InterfaceType(cls, arguments.toLink());
         }
       } else if (element.isTypedef()) {
-        // TODO(ngeoffray): This is a hack to help us get support for the
-        // DOM library.
-        // TODO(ngeoffray): The list of types for the argument is wrong.
-        type = new FunctionType(compiler.types.dynamicType,
-                                const EmptyLink<Type>(),
-                                element);
+        type = element.computeType(compiler);
       } else if (element.isTypeVariable()) {
         type = element.computeType(compiler);
       } else {
@@ -1776,6 +1775,23 @@
                                  returnType);
   }
 
+  static FunctionSignature analyzeTypedef(Compiler compiler,
+                                          TypedefElement element) {
+    Typedef node =
+          compiler.parser.measure(() => element.parseNode(compiler));
+    SignatureResolver visitor = new SignatureResolver(compiler, element);
+    Link<Node> nodes = node.formals.nodes;
+    LinkBuilder<Element> parametersBuilder = visitor.analyzeNodes(nodes);
+    Link<Element> parameters = parametersBuilder.toLink();
+    Type returnType =
+        compiler.resolveTypeAnnotation(element, node.returnType);
+    return new FunctionSignature(parameters,
+                                 visitor.optionalParameters,
+                                 parametersBuilder.length,
+                                 visitor.optionalParameterCount,
+                                 returnType);
+  }
+
   // TODO(ahe): This is temporary.
   void resolveExpression(Node node) {
     if (node == null) return;