Improve error handling in the process library.

runtime/bin/gen_snapshot.cc

 // 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.
 
 // Generate a snapshot file after loading all the scripts specified on the
 // command line.
 
-#include <assert.h>
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
 
 #include "include/dart_api.h"
 
 #include "bin/builtin.h"
 #include "bin/file.h"
 #include "bin/globals.h"
 #include "bin/process_script.h"
@@ skipping 158 matching lines @@
   // and writes out a snapshot.
   Dart_Isolate isolate = Dart_CreateIsolate(NULL, script_name);
   if (isolate == NULL) {
     return 255;
   }
 
   // Shutdown the isolate.
   Dart_ShutdownIsolate();
   return 0;
 }