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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
&Ws::SetBackgroundThrottling)
      .SetMethod("getProcessId", &Ws::GetProcessID)
      .SetMethod("getOSProcessId", &Ws::GetOSProcessID)
      .SetMethod("_getOSProcessIdForFrame",
                 &Ws::GetOSProcessIdForFrame)
      .SetMethod("equal", &Ws::Equal)
      .SetMethod("_loadURL", &Ws::LoadURL)
      .SetMethod("downloadURL", &Ws::DownloadURL)
      .SetMethod("_getURL", &Ws::GetURL)
      .SetMethod("getTitle", &Ws::GetTitle)
      .SetMethod("isLoading", &Ws::IsLoading)
      .SetMethod("isLoadingMainFrame", &Ws::IsLoadingMainFrame)
      .SetMethod("isWaitingForResponse", &Ws::IsWaitingForResponse)
      .SetMethod("_stop", &Ws::Stop)
      .SetMethod("_goBack", &Ws::GoBack)
      .SetMethod("_goForward", &Ws::GoForward)
      .SetMethod("_goToOffset", &Ws::GoToOffset)
      .SetMethod("isCrashed", &Ws::IsCrashed)
      .SetMethod("_setUserAgent", &Ws::SetUserAgent)
      .SetMethod("_getUserAgent", &Ws::GetUserAgent)
      .SetProperty("userAgent", &Ws::GetUserAgent,
                   &Ws::SetUserAgent)
      .SetMethod("savePage", &Ws::SavePage)
      .SetMethod("openDevTools", &Ws::OpenDevTools)
      .SetMethod("closeDevTools", &Ws::CloseDevTools)
      .SetMethod("isDevToolsOpened", &Ws::IsDevToolsOpened)
      .SetMethod("isDevToolsFocused", &Ws::IsDevToolsFocused)
      .SetMethod("enableDeviceEmulation", &Ws::EnableDeviceEmulation)
      .SetMethod("disableDeviceEmulation", &Ws::DisableDeviceEmulation)
      .SetMethod("toggleDevTools", &Ws::ToggleDevTools)