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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
// Is the orientation landscape or portrait.
  bool landscape = false;
  options.Get("landscape", &landscape);
  settings.SetBoolKey(printing::kSettingLandscape, landscape);
  // We set the default to the system's default printer and only update
  // if at the Chromium level if the user overrides.
  // Printer device name as opened by the OS.
  base::string16 device_name;
  options.Get("deviceName", &device_name);
  if (!device_name.empty() && !IsDeviceNameValid(device_name)) {
    args->ThrowError("ws.print(): Invalid deviceName provided.");
    return;
  }
  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);