Added slow_assert macro and flag for slow development assertions in the VM.

tools/slow_assert.py

+#!/usr/bin/env python
+# 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.
+
+import subprocess
+import sys
+
+
+def Main():
+  dart = sys.argv[1]
+  args = sys.argv[2:]
+  if args[0].startswith("--"):
+      command = [dart, "--slow-assert"] + args
+  else:
+      ## We are running a C++ test for the VM.
+      command = [dart] + args
+  exit_code = subprocess.call(command)
+  return exit_code
+
+
+if __name__ == '__main__':
+  sys.exit(Main())