Steps to reproduce the problem:
Load a remote DevTools front-end in a webview (same Electron version on both ends)

What is the expected behavior?
Remote DevTools is opened in the webview

What went wrong?
"Uncaught TypeError: Cannot read property 'extensions' of undefined".
At this point, it tries to access window.runtime.extensions("settings").
See screenshot.

Did this work before? Yes 51.0.2704.63

Chrome version: 52.0.2743.82
OS Version: OS X 10.11.4

Worked fine until Electron 1.2.0 (Chromium 51.0.2704.63) with the disablewebsecurity attribute set. Broken on 1.2.1.
Current chromium version (1.3.0): 52.0.2743.82

![screen shot 2016-07-25 at 5 36 13 pm](https://cloud.githubusercontent.com/assets/1028286/17125639/1a265cce-52aa-11e6-8413-2d75c642dbb2.png)

atom/common/node_bindings.cc
DCHECK(!is_browser_ || BrowserThread::CurrentlyOn(BrowserThread::UI));
  
  message_loop_ = base::MessageLoop::current();
  
  UvRunOnce();
}
void NodeBindings::UvRunOnce() {
  DCHECK(!is_browser_ || BrowserThread::CurrentlyOn(BrowserThread::UI));
  node::Environment* env = uv_env();
  
  mate::Locker locker(env->isolate());
  v8::HandleScope handle_scope(env->isolate());
  
  v8::Context::Scope context_scope(env->context());
  
  v8::MicrotasksScope script_scope(env->isolate(),
                                   v8::MicrotasksScope::kRunMicrotasks);
  
  int r = uv_run(uv_loop_, UV_RUN_NOWAIT);
  if (r == 0 || uv_loop_->stop_flag != 0)
    message_loop_->QuitWhenIdle();  
  
  uv_sem_post(&embed_sem_);
}
void NodeBindings::WakeupMainThread() {