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* Electron version: 1.7.0
* Operating system: macOS

### Expected behavior
Electron works with `--debug` or `-debug` argument

<!-- What do you think should happen? -->

### Actual behavior
Electron won't run with arguments above.

<!-- What actually happens? -->

### How to reproduce

I've tried the standalone .app and the npm modules:

- for standalone .app it shows an error and returns a non-zero
(with "IOVARendererID property not found" the welcome window appears and I've manually close it)
![image](https://cloud.githubusercontent.com/assets/3816900/25955449/e4d09a72-369b-11e7-894b-415231293022.png)

- for npm module it just won't start and no error returns
![image](https://cloud.githubusercontent.com/assets/3816900/25955695/84b36dee-369c-11e7-9d19-6014f13d9a50.png)


I can confirm the `--debug` works with previous versions including 1.6.9 beta

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atom/app/node_main.cc
base::CommandLine::Init(argc, argv);
  int exit_code = 1;
  {
    
    argv = uv_setup_args(argc, argv);
    uv_loop_t* loop = uv_default_loop();
    scoped_refptr<UvTaskRunner> uv_task_runner(new UvTaskRunner(loop));
    base::ThreadTaskRunnerHandle handle(uv_task_runner);
    
    std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
    feature_list->InitializeFromCommandLine("", "");
    base::FeatureList::SetInstance(std::move(feature_list));
    gin::V8Initializer::LoadV8Snapshot();
    gin::V8Initializer::LoadV8Natives();
    JavascriptEnvironment gin_env;
    int exec_argc;
    const char** exec_argv;
    node::Init(&argc, const_cast<const char**>(argv), &exec_argc, &exec_argv);
    node::IsolateData isolate_data(gin_env.isolate(), loop);
    node::Environment* env = node::CreateEnvironment(
        &isolate_data, gin_env.context(), argc, argv,
        exec_argc, exec_argv);
    
    NodeDebugger node_debugger(gin_env.isolate());
    if (node_debugger.IsRunning())
      env->AssignToContext(v8::Debug::GetDebugContext(gin_env.isolate()));
    mate::Dictionary process(gin_env.isolate(), env->process_object());