Fix bug with missing unboxed mint-to-double conversion.

tests/language/mint_arithmetic.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.
 
 // Test arithmetic on 64-bit integers.
 
 test_and_1() {
   try {  // Avoid optimizing this function.
     f(a, b) {
       var s = b;
@@ skipping 48 matching lines @@
     }
     var x = 0xffffffff;
     for (var i = 0; i < 10000; i++) f(x, x);
     Expect.equals(x, f(x, x));
     Expect.equals(-1, f(x, -1));
     var y  = 0xffffffffffffffff;
     Expect.equals(-1, f(y, -1));  // Triggers deoptimization.
   } finally { }
 }
 
+test_func(x, y) => (x & y) + 1.0;
+
+test_mint_double_op() {
+  for (var i=0; i<10000; i++) test_func(4294967295, 1);
+  Expect.equals(2.0, test_func(4294967295, 1));
+  Expect.equals(4294967296.0, test_func(4294967295, 1));
+}
+
 main() {
   for (var i = 0; i < 5; i++) {
     test_and_1();
     test_and_2();
     test_xor_1();
     test_or_1();
+    test_mint_double_op();
   }
 }