Electron Version: 7.1.1
Operating System: Windows 10 (1803)

If I set the 'margins' option when call webContents.print method,
The app will crash with no error message.

```js
let { remote } = require("electron");
let webContents = remote.getCurrentWebContents();
webContents.print(
  {
    margins: {
      marginType: "custom",
      top: 30,
      bottom: 0,
      left: 0,
      right: 0
    }
  },
  (success, errorType) => {
    if (!success) console.log(errorType);
  }
);
```

shell/browser/api/electron_api_web_contents.cc
const GURL& url) {
  Emit("update-target-url", url);
}
bool Ws::HandleKeyboardEvent(
    content::Ws* source,
    const content::NativeWebKeyboardEvent& event) {
  if (type_ == Type::WEB_VIEW && embedder_) {
    
    return embedder_->HandleKeyboardEvent(source, event);
  } else {
    
    return CommonWsDelegate::HandleKeyboardEvent(source, event);
  }
}
content::KeyboardEventProcessingResult Ws::PreHandleKeyboardEvent(
    content::Ws* source,
    const content::NativeWebKeyboardEvent& event) {
  if (event.GetType() == blink::WebInputEvent::Type::kRawKeyDown ||
      event.GetType() == blink::WebInputEvent::Type::kKeyUp) {
    bool prevent_default = Emit("before-input-event", event);
    if (prevent_default) {
      return content::KeyboardEventProcessingResult::HANDLED;
    }
  }
  return content::KeyboardEventProcessingResult::NOT_HANDLED;
}
void Ws::ContentsZoomChange(bool zoom_in) {