### Preflight Checklist

- [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](https://www.github.com/electron/electron/issues) for a feature request that matches the one I want to file, without success.

### Problem Description

We need to load a custom error page when the certificate is invalid but without "isMainFrame" property we don't know when to load the custom error page using webContents.loadURL()

### Proposed Solution

webContents.on("certificate-error", ((event, url, error, certificate, callback, isMainFrame)

### Alternatives Considered

Not sure

### Additional Information

Not sure
shell/browser/api/electron_api_app.cc
.SetMethod("showEmojiPanel",
                 base::BindRepeating(&Browser::ShowEmojiPanel, browser))
#endif
#if defined(OS_WIN)
      .SetMethod("setUserTasks",
                 base::BindRepeating(&Browser::SetUserTasks, browser))
      .SetMethod("getJumpListSettings", &App::GetJumpListSettings)
      .SetMethod("setJumpList", &App::SetJumpList)
#endif
#if defined(OS_LINUX)
      .SetMethod("isUnityRunning",
                 base::BindRepeating(&Browser::IsUnityRunning, browser))
#endif
      .SetProperty("isPackaged", &App::IsPackaged)
      .SetMethod("setAppPath", &App::SetAppPath)
      .SetMethod("getAppPath", &App::GetAppPath)
      .SetMethod("setPath", &App::SetPath)
      .SetMethod("getPath", &App::GetPath)
      .SetMethod("setAppLogsPath", &App::SetAppLogsPath)
      .SetMethod("setDesktopName", &App::SetDesktopName)
      .SetMethod("getLocale", &App::GetLocale)
      .SetMethod("getLocaleCountryCode", &App::GetLocaleCountryCode)
#if defined(USE_NSS_CERTS)
      .SetMethod("importCertificate", &App::ImportCertificate)
#endif
      .SetMethod("hasSingleInstanceLock", &App::HasSingleInstanceLock)
      .SetMethod("requestSingleInstanceLock", &App::RequestSingleInstanceLock)
      .SetMethod("releaseSingleInstanceLock", &App::ReleaseSingleInstanceLock)
      .SetMethod("relaunch", &App::Relaunch)
      .SetMethod("isAccessibilitySupportEnabled",