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
#include "third_party/blink/public/common/page/page_zoom.h"
#include "third_party/blink/public/mojom/frame/find_in_page.mojom.h"
#include "third_party/blink/public/mojom/frame/fullscreen.mojom.h"
#include "third_party/blink/public/platform/ursor_info.h"
#include "ui/display/screen.h"
#include "ui/events/base_event_utils.h"
#if BUILDFLAG(ENABLE_OSR)
#include "shell/browser/osr/osr_render_widget_host_view.h"
#include "shell/browser/osr/osr_ontents_view.h"
#endif
#if !defined(OS_MACOSX)
#include "ui/aura/window.h"
#else
#include "ui/base/cocoa/defaults_utils.h"
#endif
#if defined(OS_LINUX)
#include "ui/views/linux_ui/linux_ui.h"
#endif
#if defined(OS_LINUX) || defined(OS_WIN)
#include "third_party/blink/public/mojom/renderer_preferences.mojom.h"
#include "ui/gfx/font_render_params.h"
#endif
#if BUILDFLAG(ENABLE_ELECTRON_EXTENSIONS)
#include "shell/browser/extensions/electron_extension_ontents_observer.h"
#endif
namespace gin {
#if BUILDFLAG(ENABLE_PRINTING)
template <>
struct Converter<printing::PrinterBasicInfo> {
  static v8::Local<v8::Value> ToV8(v8::Isolate* isolate,