* 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
}
void AtomSandboxedRendererClient::RenderFrameCreated(
    content::RenderFrame* render_frame) {
  new AtomSandboxedRenderFrameObserver(render_frame, this);
  RendererClientBase::RenderFrameCreated(render_frame);
}
void AtomSandboxedRendererClient::RenderViewCreated(
    content::RenderView* render_view) {
  RendererClientBase::RenderViewCreated(render_view);
}
void AtomSandboxedRendererClient::DidCreateScriptContext(
    v8::Handle<v8::Context> context, content::RenderFrame* render_frame) {
  
  if (!render_frame->IsMainFrame())
    return;
  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
  base::FilePath preload_script_path = command_line->GetSwitchValuePath(
      switches::kPreloadScript);
  if (preload_script_path.empty())
    return;
  auto isolate = context->GetIsolate();
  v8::HandleScope handle_scope(isolate);
  v8::Context::Scope context_scope(context);
  
  
  std::string preload_bundle_native(node::preload_bundle_data,
      node::preload_bundle_data + sizeof(node::preload_bundle_data));
  std::stringstream ss;
  ss << "(function(binding, preloadPath, require) {\n";