Explicitly use node.js in the cases where it is needed.

dart/frog/scripts/bootstrap/frog_wrapper.py

 #!/usr/bin/env python
 # 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.
 
 import imp
 import os
 import sys
 
 def main(args):
   # Try to find frog.py from the current location.
   home = os.path.join(os.curdir, 'frog.py')
   if not os.path.exists(home):
     home = os.path.join(os.curdir, 'frog', 'frog.py')
 
   if not os.path.exists(home):
     print "Could not find frog"
     return 1
 
-  frog_args = [ 'frog.py', '--vm=' + VM ]
+  frog_args = [ 'frog.py', '--vm=%s' % VM]
+  js_cmd_flag = '--js_cmd=%s --crankshaft' % D8
+  for arg in args:
+    if arg.startswith('--js_cmd'):
+      js_cmd_flag = arg
+  if js_cmd_flag in args:
+    args.remove(js_cmd_flag)
+  frog_args.append(js_cmd_flag)
   if VM_FLAGS:
     frog_args.append(VM_FLAGS)
   frog_args.append('--')
   frog_args.extend(args[1:])
 
   filename = None
   exit_code = 1
   try:
     # Load frog.py and invoke it.
     paths = [os.path.dirname(home)]
     (filename, pathname, description) = imp.find_module('frog', paths)
     module = imp.load_module('frog', filename, pathname, description)
     exit_code = module.main(frog_args)
   finally:
     if filename:
       filename.close()
 
   return exit_code