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* Electron version: 1.7.2
* Operating system: macOS Sierra

### Expected behavior

Webview appear

### Actual behavior

It don't

### How to reproduce

1. Create a browser window with contextIsolation on true and webviewTag on true
2. Inside of it, add a webview
3. Run it, webview should not appear

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atom/renderer/atom_renderer_client.cc
if (!(render_frame->IsMainFrame() &&
        !render_frame->GetWebFrame()->Opener()) &&
      !IsDevToolsExtension(render_frame))
    return;
  injected_frames_.insert(render_frame);
  
  if (!node_integration_initialized_) {
    node_integration_initialized_ = true;
    node_bindings_->Initialize();
    node_bindings_->PrepareMessageLoop();
  }
  
  if (!node::tracing::TraceEventHelper::GetAgent())
    node::tracing::TraceEventHelper::SetAgent(node::CreateAgent());
  
  node::Environment* env = node_bindings_->CreateEnvironment(context);
  environments_.insert(env);
  
  atom_bindings_->BindTo(env->isolate(), env->process_object());
  AddRenderBindings(env->isolate(), env->process_object());
  
  node_bindings_->LoadEnvironment(env);
  if (node_bindings_->uv_env() == nullptr) {
    
    node_bindings_->set_uv_env(env);
    
    node_bindings_->RunMessageLoop();
  }
}
void AtomRendererClient::WillReleaseScriptContext(