* Electron version: 1.7.9
* Operating system: macOS 10.13.1

### Expected behavior

If pinch-zoom is disabled via `webFrame.setVisualZoomLevelLimits(1, 1);` it should stay disabled.

### Actual behavior

Pinch zoom is possible. 

### How to reproduce

* connect an external monitor and open any electron app there, keep the macbook pro lid closed
* disconnect the external monitor
* open the lid

=> you can now pinch zoom 
atom/renderer/api/atom_api_web_frame.cc
mate::Arguments* args) {
  bool has_user_gesture = false;
  args->GetNext(&has_user_gesture);
  ScriptExecutionCallback::CompletionCallback completion_callback;
  args->GetNext(&completion_callback);
  std::unique_ptr<blink::WebScriptExecutionCallback> callback(
      new ScriptExecutionCallback(completion_callback));
  web_frame_->RequestExecuteScriptAndReturnValue(
      blink::WebScriptSource(blink::WebString::FromUTF16(code)),
      has_user_gesture,
      callback.release());
}
void WebFrame::ExecuteJavaScriptInIsolatedWorld(
    int world_id,
    const std::vector<mate::Dictionary>& scripts,
    mate::Arguments* args) {
  std::vector<blink::WebScriptSource> sources;
  for (const auto& script : scripts) {
    base::string16 code;
    base::string16 url;
    int start_line = 1;
    script.Get("url", &url);
    script.Get("startLine", &start_line);
    if (!script.Get("code", &code)) {
      args->ThrowError("Invalid 'code'");
      return;
    }
    sources.emplace_back(blink::WebScriptSource(
            blink::WebString::FromUTF16(code),