* Electron version: 1.7.6
* Operating system: macOS 10.12, Windows 10

### Expected behavior

Right clicking should open context menu in devtools

### Actual behavior

Right clicking does not open the context menu in devtools

### How to reproduce

- `open Electron.app --args --enable-mixed-sandbox`
- open devtools
- right click in the source tab for example
atom/renderer/atom_sandboxed_renderer_client.cc
ss << preload_bundle_native << "\n";
  ss << "})";
  std::string preload_wrapper = ss.str();
  
  auto script = v8::Script::Compile(
      mate::ConvertToV8(isolate, preload_wrapper)->ToString());
  auto func = v8::Handle<v8::Function>::Cast(
      script->Run(context).ToLocalChecked());
  
  auto binding = v8::Object::New(isolate);
  InitializeBindings(binding, context);
  AddRenderBindings(isolate, binding);
  v8::Local<v8::Value> args[] = {
    binding,
    mate::ConvertToV8(isolate, preload_script_path.value())
  };
  
  ignore_result(func->Call(context, v8::Null(isolate), 2, args));
}
void AtomSandboxedRendererClient::WillReleaseScriptContext(
    v8::Handle<v8::Context> context, content::RenderFrame* render_frame) {
  
  if (!render_frame->IsMainFrame())
    return;
  auto isolate = context->GetIsolate();
  v8::HandleScope handle_scope(isolate);
  v8::Context::Scope context_scope(context);
  InvokeIpcCallback(context, "onExit", std::vector<v8::Local<v8::Value>>());
}
void AtomSandboxedRendererClient::InvokeIpcCallback(