* **Electron Version** 4.0.4
* **Operating System** Windows 10 32 bit
* **Last known working Electron version** 3.1.3

### Expected Behavior
`webContents.print()` shold send print job to a printer

### Actual behavior
Nothing happens. Callback doesn't gets called. 

`printToPDF` works though.

### To Reproduce
```
let deviceName = 'HP LaserJet 1020'
let options = {deviceName, silent: true}
win.webContents.print({}, (err) => {
    if (!err)
      console.error('printing failed')
})
```

atom/browser/api/atom_api_web_contents.cc
v8::Local<v8::Value> val,
                     content::SavePageType* out) {
    std::string save_type;
    if (!ConvertFromV8(isolate, val, &save_type))
      return false;
    save_type = base::ToLowerASCII(save_type);
    if (save_type == "htmlonly") {
      *out = content::SAVE_PAGE_TYPE_AS_ONLY_HTML;
    } else if (save_type == "htmlcomplete") {
      *out = content::SAVE_PAGE_TYPE_AS_COMPLETE_HTML;
    } else if (save_type == "mhtml") {
      *out = content::SAVE_PAGE_TYPE_AS_MHTML;
    } else {
      return false;
    }
    return true;
  }
};
template <>
struct Converter<atom::api::WebContents::Type> {
  static v8::Local<v8::Value> ToV8(v8::Isolate* isolate,