Support for "a is Function".

tests/language/src/IsFunctionTest.dart

 // Copyright (c) 2012, 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.
 
-typedef void MyFunctionType();
-
-class A native "*A" {
-  setClosure(MyFunctionType f) native;
-  check(MyFunctionType f) native;
-  invoke() native;
-}
-
-makeA() native { return new A(); }
-
-void setup() native """
-function A() {}
-A.prototype.setClosure = function(f) { this.f = f; };
-A.prototype.check = function(f) { return this.f === f; };
-A.prototype.invoke = function() { return this.f(); };
-makeA = function(){return new A;};
-""";
-
 var staticClosure;
 staticMethod() => 42;
 
 class B {
   var instanceClosure;
+  var nullField;
   instanceMethod() => 43;
 }
 
-checkUntyped(a, closure) {
-  a.setClosure(closure);
-  Expect.isTrue(a.check(closure));
-  Expect.equals(closure(), a.invoke());
+checkUntyped(closure) {
+  Expect.isTrue(closure is Function);
 }
 
-checkTyped(A a, MyFunctionType closure) {
-  a.setClosure(closure);
-  Expect.isTrue(a.check(closure));
-  Expect.equals(closure(), a.invoke());
+checkTyped(int closure()) {
+  Expect.isTrue(closure is Function);
+}
+
+checkTypedNull(int closure()) {
+  Expect.isFalse(closure is Function);
+}
+
+checkUntypedNull(closure) {
+  Expect.isFalse(closure is Function);
 }
 
 main() {
-  setup();
-
   staticClosure = () => 44;
   B b = new B();
   b.instanceClosure = () => 45;
 
   closureStatement() => 46;
   var closureExpression = () => 47;
 
-  checkUntyped(makeA(), staticClosure);
-  checkTyped(makeA(), staticClosure);
+  checkUntyped(staticClosure);
+  checkTyped(staticClosure);
 
-  checkUntyped(makeA(), staticMethod);
-  checkTyped(makeA(), staticMethod);
+  checkUntyped(staticMethod);
+  checkTyped(staticMethod);
 
-  checkUntyped(makeA(), b.instanceClosure);
-  checkTyped(makeA(), b.instanceClosure);
+  checkUntyped(b.instanceClosure);
+  checkTyped(b.instanceClosure);
 
-  checkUntyped(makeA(), b.instanceMethod);
-  checkTyped(makeA(), b.instanceMethod);
+  checkUntyped(b.instanceMethod);
+  checkTyped(b.instanceMethod);
 
-  checkUntyped(makeA(), closureStatement);
-  checkTyped(makeA(), closureStatement);
+  checkUntyped(closureStatement);
+  checkTyped(closureStatement);
 
-  checkUntyped(makeA(), closureExpression);
-  checkTyped(makeA(), closureExpression);
+  checkUntyped(closureExpression);
+  checkTyped(closureExpression);
+
+  checkTypedNull(b.nullField);
+  checkUntypedNull(b.nullField);
 }