Add function parameter info in docgen.

pkg/docgen/lib/src/models/closure.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 docgen.models.closure;
+
+import '../exports/source_mirrors.dart';
+
+import 'doc_gen_type.dart';
+import 'indexable.dart';
+import 'mirror_based.dart';
+import 'model_helpers.dart';
+import 'parameter.dart';
+
+/// A class containing the properties of a function to be called (used in our
+/// case specifically to illustrate evidence of the type of function for a
+/// parameter).
+class Closure extends MirrorBased<FunctionTypeMirror> {
+
+  /// Parameters for this method.
+  final Map<String, Parameter> parameters;
+  final DocGenType returnType;
+  final FunctionTypeMirror mirror;
+
+  Closure(FunctionTypeMirror mirror, Indexable owner)
+    : returnType = new DocGenType(mirror.returnType, owner.owningLibrary),
+      parameters = createParameters(mirror.parameters, owner),
+      mirror = mirror;
+
+  /// Generates a map describing the [Method] object.
+  Map toMap() => {
+    'return': [returnType.toMap()],
+    'parameters': recurseMap(parameters),
+  };
+}