### Preflight Checklist
* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

* **Electron Version:**
  5.0.1
* **Operating System:**
  windows
* **Last Known Working Electron version:**
  n/a

### Expected Behavior
A preload script should run only 1 time for each webContents / iframe

### Actual Behavior
The preload script appears to run multiple times

### To Reproduce
https://github.com/Tim91084/electron-node-subframe-issue/tree/node-in-subframe-runs-too-often

```sh
$ git clone https://github.com/Tim91084/electron-node-subframe-issue.git -b node-in-subframe-runs-too-often
$ npm install
$ npm start || electron .
```

### Screenshots
![image](https://user-images.githubusercontent.com/5086428/58273769-63b9d900-7d5f-11e9-8d30-1525dea34ce3.png)

shell/renderer/atom_renderer_client.cc
v8::Handle<v8::Context> context,
    content::RenderFrame* render_frame,
    int world_id) {
  auto* isolate = context->GetIsolate();
  std::vector<v8::Local<v8::String>> isolated_bundle_params = {
      node::FIXED_ONE_BYTE_STRING(isolate, "nodeProcess"),
      node::FIXED_ONE_BYTE_STRING(isolate, "isolatedWorld"),
      node::FIXED_ONE_BYTE_STRING(isolate, "worldId")};
  auto* env = GetEnvironment(render_frame);
  if (!env)
    return;
  std::vector<v8::Local<v8::Value>> isolated_bundle_args = {
      env->process_object(),
      GetContext(render_frame->GetWebFrame(), isolate)->Global(),
      v8::Integer::New(isolate, world_id)};
  node::native_module::NativeModuleEnv::CompileAndCall(
      context, "electron/js2c/content_script_bundle", &isolated_bundle_params,
      &isolated_bundle_args, nullptr);
}
node::Environment* AtomRendererClient::GetEnvironment(