Detect crashes in frog/leg (when running on VM).

dart/frog/minfrogc.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.
 
 #library('minfrogc');
 
 #import('file_system_vm.dart');
 #import('lang.dart');
 
 main() {
@@ skipping 11 matching lines @@
 
   // TODO(dgrove) we're simulating node by placing the arguments to frogc
   // starting at index 2.
   argv.insertRange(0, 2, null);
 
   // TODO(dgrove) Until we have a way of getting the executable's path, we'll
   // run from '.'
   var homedir = (new File('.')).fullPathSync();
 
   if (!compile(homedir, argv, new VMFileSystem())) {
-    throw "Compilation failed";
+    print("Compilation failed");
+    exit(1);
   }
 }