Use JavaScript runtime semantics when constant folding.

tests/corelib/expression_test.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 basic expressions. Does not attempt to validate the details of arithmetic, coercion, and
 // so forth.
 class ExpressionTest {
 
   ExpressionTest() {}
 
@@ skipping 12 matching lines @@
   testBinary() {
     int x = 4, y = 2;
     Expect.equals(6, x + y);
     Expect.equals(2, x - y);
     Expect.equals(8, x * y);
     Expect.equals(2, x / y);
     Expect.equals(0, x % y);
   }
 
   testUnary() {
-    int x = 4, y = 2;
+    int x = 4, y = 2, z = -5;
     bool t = true, f = false;
     Expect.equals(-4, -x);
-    Expect.equals(-5, ~x);
+    Expect.equals(4, ~z);
     Expect.equals(f, !t);
   }
 
   testShifts() {
     int x = 4, y = 2;
     Expect.equals(y, x >> 1);
     Expect.equals(x, y << 1);
   }
 
   testBitwise() {
@@ skipping 60 matching lines @@
     this[0] = 0;
     Expect.equals(42, (this[0] += $0));
     Expect.equals(129, (this[0] += $1));
     Expect.equals(246, (this[0] += $2));
   }
 }
 
 main() {
   ExpressionTest.testMain();
 }