### 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
if (Emit("will-quit")) {
    *prevent_default = true;
  }
}
void App::OnWindowAllClosed() {
  Emit("window-all-closed");
}
void App::OnQuit() {
  const int exitCode = ElectronBrowserMainParts::Get()->GetExitCode();
  Emit("quit", exitCode);
  if (process_singleton_) {
    process_singleton_->Cleanup();
    process_singleton_.reset();
  }
}
void App::OnOpenFile(bool* prevent_default, const std::string& file_path) {
  if (Emit("open-file", file_path)) {
    *prevent_default = true;
  }
}
void App::OnOpenURL(const std::string& url) {
  Emit("open-url", url);
}
void App::OnActivate(bool has_visible_windows) {
  Emit("activate", has_visible_windows);
}
void App::OnWillFinishLaunching() {
  Emit("will-finish-launching");
}
void App::OnFinishLaunching(const base::DictionaryValue& launch_info) {