Make is checks work on JavaScriptFunction objects.

pkg/compiler/lib/src/js_backend/js_interop_analysis.dart

 // Copyright (c) 2015, 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.
 
 /// Analysis to determine how to generate code for typed JavaScript interop.
 library compiler.src.js_backend.js_interop_analysis;
 
 import '../common.dart';
 import '../constants/values.dart'
     show ConstantValue, ConstructedConstantValue, StringConstantValue;
+import '../dart_types.dart'
+    show
+        DartType,
+        DynamicType,
+        FunctionType;
 import '../diagnostics/messages.dart' show MessageKind;
 import '../elements/elements.dart'
     show
         ClassElement,
         Element,
         FieldElement,
         FunctionElement,
         LibraryElement,
         ParameterElement,
         MetadataAnnotation;
@@ skipping 157 matching lines @@
 
           var name = backend.namer.invocationName(selector);
           statements.add(js.statement(
               'Function.prototype.# = function(#) { return this(#) }',
               [name, parameters, parameters]));
         }
       });
     });
     return new jsAst.Block(statements);
   }
+
+  FunctionType buildJsFunctionType() {
+    // TODO(jacobr): consider using codegenWorld.isChecks to determine the
+    // range of positional arguments that need to be supported by JavaScript
+    // function types.
+    return new FunctionType.synthesized(
+      const DynamicType(),
+      [],
+      new List<DartType>.generate(16, (_) => const DynamicType()));

[sra1, 2016/06/30 17:57:13]

This is ok since it is a one-of thing, but consider List.filled.

[Jacob, 2016/07/01 18:27:50]

filled is better. Forgot we had that constructor.

+  }
 }