DBC: Enables unboxed doubles

runtime/tests/vm/dart/double_materialize_test.dart

+// Copyright (c) 2016, 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.
+
+// VMOptions=--optimization_counter_threshold=10 --no-use-osr --no-background-compilation
+
+import "package:expect/expect.dart";
+
+double f(double x, double five, dynamic y) {
+  double z = x + five;
+  var a = y + 5;
+  return z + a.toDouble();
+}
+
+void main() {
+  double x = 1.0;
+  for (int i = 0; i < 1000; i++) {
+    x = f(x, 5.0, i);
+  }
+  x = f(x, 5.0, 1.0);
+  Expect.equals(509512.0, x);
+}
+