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

runtime/lib/integers.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.
 
 // TODO(srdjan): fix limitations.
 // - shift amount must be a Smi.
 class IntegerImplementation {
   num operator +(num other) {
     return other.addFromInteger(this);
   }
@@ skipping 74 matching lines @@
   int abs() {
     return this < 0 ? -this : this;
   }
   bool isEven() { return ((this & 1) === 0); }
   bool isOdd() { return !isEven(); }
   bool isNaN() { return false; }
   bool isNegative() { return this < 0; }
   bool isInfinite() { return false; }
 
   int compareTo(Comparable other) {
-    if (this == other) return 0;
-    if (this < other) return -1;
-    return 1;
+    final int EQUAL = 0, LESS = -1, GREATER = 1;
+    if (this < other) {
+      return LESS;
+    } else if (this > other) {
+      return GREATER;
+    } else if (this == other) {
+      return EQUAL;
+    } else {
+      // Other is NaN.
+      return LESS;
+    }
   }
+
   int round() { return this; }
   int floor() { return this; }
   int ceil() { return this; }
   int truncate() { return this; }
 
   int toInt() { return this; }
   double toDouble() { return new Double.fromInteger(this); }
 
   int pow(int exponent) {
     throw "IntegerImplementation.pow not implemented";
@@ skipping 64 matching lines @@
     if (other < 0) {
       return -1;
     } else {
       return 0;
     }
   }
   int shlFromInt(int other) {
     throw const OutOfMemoryException();
   }
 }