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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 a feature request that matches the one I want to file, without success.

### Problem Description
<!-- Is your feature request related to a problem? Please add a clear and concise description of what the problem is. -->

They is no way to choose the paper format (A4, A3, Letter, ...) when printing with `webContents.print()`.

### Proposed Solution
<!-- Describe the solution you'd like in a clear and concise manner -->

Add something like the `pageSize` option which is available in [`webContents.printToPDF()`](https://electronjs.org/docs/api/web-contents#contentsprinttopdfoptions-callback).

shell/browser/api/electron_api_web_contents.cc
// Set custom margin settings
  gin_helper::Dictionary margins =
      gin::Dictionary::CreateEmpty(args->isolate());
  if (options.Get("margins", &margins)) {
    printing::MarginType margin_type = printing::DEFAULT_MARGINS;
    margins.Get("marginType", &margin_type);
    settings.SetIntKey(printing::kSettingMarginsType, margin_type);
    if (margin_type == printing::CUSTOM_MARGINS) {
      int top = 0;
      margins.Get("top", &top);
      settings.SetIntKey(printing::kSettingMarginTop, top);
      int bottom = 0;
      margins.Get("bottom", &bottom);
      settings.SetIntKey(printing::kSettingMarginBottom, bottom);
      int left = 0;
      margins.Get("left", &left);
      settings.SetIntKey(printing::kSettingMarginLeft, left);
      int right = 0;
      margins.Get("right", &right);
      settings.SetIntKey(printing::kSettingMarginRight, right);
    }
  } else {
    settings.SetIntKey(printing::kSettingMarginsType,
                       printing::DEFAULT_MARGINS);
  }
  // Set whether to print color or greyscale
  bool print_color = true;
  options.Get("color", &print_color);
  int color_setting = print_color ? printing::COLOR : printing::GRAY;
  settings.SetIntKey(printing::kSettingColor, color_setting);