Use JavaScript runtime semantics when constant folding.

tests/compiler/dart2js_extra/constant_javascript_semantics_test.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.
+
+// Make sure we use JavaScript semantics when compiling compile-time constants.
+
+const x = 12345678901234567891;
+const y = 12345678901234567890;
+const z = x - y;
+
+const a = 1.0;
+const b = a << 3;  // This would not be valid with Dart semantics.
+
+const c = -0.0;
+const d = c << 1;  // This would not be valid with Dart semantics.
+
+foo() => 12345678901234567891 - 12345678901234567890;
+
+main() {
+  Expect.equals(0, z);
+  Expect.equals(0, x - y);
+  Expect.equals(0, foo());
+  Expect.isTrue(x is double);
+  // TODO(floitsch): we probably want to change this to be true.
+  Expect.isFalse(x is int);
+  Expect.equals(8, b);
+  Expect.equals(8, 1.0 << 3);  // This would not be valid with Dart semantics.
+  Expect.isTrue(1 == 1.0);
+  Expect.equals(0, d);
+  Expect.equals(0, -0.0 << 1);  // This would not be valid with Dart semantics.
+  // Make sure the 1 is not shifted into the 32 bit range.
+  Expect.equals(0, 0x100000000 >> 3);
+  // The dynamic int-check also allows -0.0.
+  Expect.isTrue((-0.0) is int);
+}