Fix issues that caused revert of r30955:

dart/sdk/lib/_internal/lib/js_mirrors.dart

Index: dart/sdk/lib/_internal/lib/js_mirrors.dart
diff --git a/dart/sdk/lib/_internal/lib/js_mirrors.dart b/dart/sdk/lib/_internal/lib/js_mirrors.dart
index 0cb1720955cf53e019aea8cf9e8ddf8d3ff6196b..ba809de98874a716724c141d3153732464e8504d 100644
--- a/dart/sdk/lib/_internal/lib/js_mirrors.dart
+++ b/dart/sdk/lib/_internal/lib/js_mirrors.dart
@@ -1771,6 +1771,8 @@ class JsMethodMirror extends JsDeclarationMirror implements MethodMirror {
         if (functionType is int) {
           type = new JsFunctionTypeMirror(info.computeFunctionRti(null), this);
           assert(_parameterCount == type.parameters.length);
+        } else if (isTopLevel) {
+          type = new JsFunctionTypeMirror(info.computeFunctionRti(null), owner);
         } else {
           TypeMirror ownerType = owner;
           JsClassMirror ownerClass = ownerType.originalDeclaration;