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### Preflight Checklist
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* [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:**
  * v8.0.0-beta.2
* **Operating System:**
  * macOS 10.14.5
* **Last Known Working Electron version:**
  * v6.1.X 

### Expected Behavior
No warnings

### Actual Behavior
The warning

```
[28455:1113/114404.211707:ERROR:CONSOLE(3361)] "Uncaught TypeError: sender.emit is not iterable (cannot read property Symbol(Symbol.iterator))", source: electron/js2c/sandbox_bundle.js (3361)
```

is printed in the console constantly.

### To Reproduce
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```sh
$ git clone $YOUR_URL -b $BRANCH
$ npm install
$ npm start || electron .
```
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### Screenshots

![image](https://user-images.githubusercontent.com/380914/68798485-5cd39b00-060b-11ea-80d9-1f62cbb97e52.png)


shell/browser/api/atom_api_web_contents.cc
options.Get("color", &print_color);
  int color_setting = print_color ? printing::COLOR : printing::GRAY;
  settings.SetIntKey(printing::kSettingColor, color_setting);
  // Is the orientation landscape or portrait.
  bool landscape = false;
  options.Get("landscape", &landscape);
  settings.SetBoolKey(printing::kSettingLandscape, landscape);
  // We set the default to empty string here and only update
  // if at the Chromium level if it's non-empty
  // Printer device name as opened by the OS.
  base::string16 device_name;
  options.Get("deviceName", &device_name);
  settings.SetStringKey(printing::kSettingDeviceName, device_name);
  int scale_factor = 100;
  options.Get("scaleFactor", &scale_factor);
  settings.SetIntKey(printing::kSettingScaleFactor, scale_factor);
  int pages_per_sheet = 1;
  options.Get("pagesPerSheet", &pages_per_sheet);
  settings.SetIntKey(printing::kSettingPagesPerSheet, pages_per_sheet);
  // True if the user wants to print with collate.
  bool collate = true;
  options.Get("collate", &collate);
  settings.SetBoolKey(printing::kSettingCollate, collate);
  // The number of individual copies to print
  int copies = 1;
  options.Get("copies", &copies);
  settings.SetIntKey(printing::kSettingCopies, copies);
  // Strings to be printed as headers and footers if requested by the user.
  std::string header;
  options.Get("header", &header);