Fix throwing ObjectNotClosure instead of null exception if closure is null.

tests/language/src/CallThroughNullGetterTest.dart

 // Copyright (c) 2011, 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.
 
 // Tests that we can call functions through getters which return null.
 
 final TOP_LEVEL_NULL = null;
 
 var topLevel;
 
 class CallThroughNullGetterTest {
 
   static void testMain() {
     testTopLevel();
     testField();
     testGetter();
     testMethod();
   }
 
   static void testTopLevel() {
     topLevel = null;
-    expectThrowsNullPointerException(() { topLevel(); });
-    expectThrowsNullPointerException(() { (topLevel)(); });
-    expectThrowsNullPointerException(() { TOP_LEVEL_NULL(); });
-    expectThrowsNullPointerException(() { (TOP_LEVEL_NULL)(); });
+    expectThrowsObjectNotClosureException(() { topLevel(); });
+    expectThrowsObjectNotClosureException(() { (topLevel)(); });
+    expectThrowsObjectNotClosureException(() { TOP_LEVEL_NULL(); });
+    expectThrowsObjectNotClosureException(() { (TOP_LEVEL_NULL)(); });
   }
 
   static void testField() {
     A a = new A();
 
     a.field = null;
-    expectThrowsNullPointerException(() { a.field(); });
-    expectThrowsNullPointerException(() { (a.field)(); });
+    expectThrowsObjectNotClosureException(() { a.field(); });
+    expectThrowsObjectNotClosureException(() { (a.field)(); });
   }
 
   static void testGetter() {
     A a = new A();
 
     a.field = null;
-    expectThrowsNullPointerException(() { a.getter(); });
-    expectThrowsNullPointerException(() { (a.getter)(); });
+    expectThrowsObjectNotClosureException(() { a.getter(); });
+    expectThrowsObjectNotClosureException(() { (a.getter)(); });
   }
 
   static void testMethod() {
     A a = new A();
 
     a.field = null;
-    expectThrowsNullPointerException(() { a.method()(); });
+    expectThrowsObjectNotClosureException(() { a.method()(); });
   }
 
   static void expectThrowsNullPointerException(fn) {
     var exception = catchException(fn);
     if (!(exception is NullPointerException)) {
       Expect.fail("Wrong exception.  Expected: NullPointerException"
           + " got: ${exception}");
     }
   }
 
+  static void expectThrowsObjectNotClosureException(fn) {
+    var exception = catchException(fn);
+    if (!(exception is ObjectNotClosureException)) {
+      Expect.fail("Wrong exception.  Expected: ObjectNotClosureException"
+          + " got: ${exception}");
+    }
+  }
+
   static catchException(fn) {
     bool caught = false;
     var result = null;
     try {
       fn();
       Expect.equals(true, false);  // Shouldn't reach this.
     } catch (var e) {
       caught = true;
       result = e;
     }
     Expect.equals(true, caught);
     return result;
   }
 
 }
 
 
 class A {
 
   A() { }
   var field;
   get getter() { return field; }
   method() { return field; }
 
 }
 
 main() {
   CallThroughNullGetterTest.testMain();
 }