If I set the style on any text in a `BrowserWindow` as such:

```
P {
   font-family: cursive;
}
```

...I would expect that text to take on a "cursive" look, much as it does when I apply the same style to a page loaded in Chrome Browser.

However in Electron 1.4.12 on Mac it looks like it's `serif`.

`cursive` is one of the W3C's five standard styles along with `serif`, `sans-serif`, `monospace`, and `fantasy` [1]. All of these work as expected in Electron except `cursive`.

It seems it should work just like the others. I presume it's just an omission somewhere?

Thanks!

[1] https://www.w3.org/wiki/CSS/Properties/font-family
atom/browser/web_contents_preferences.cc
int process_id) {
  for (WebContentsPreferences* preferences : instances_) {
    content::WebContents* web_contents = preferences->web_contents_;
    if (web_contents->GetRenderProcessHost()->GetID() == process_id)
      return web_contents;
  }
  return nullptr;
}
void WebContentsPreferences::AppendExtraCommandLineSwitches(
    content::WebContents* web_contents, base::CommandLine* command_line) {
  WebContentsPreferences* self = FromWebContents(web_contents);
  if (!self)
    return;
  base::DictionaryValue& web_preferences = self->web_preferences_;
  bool b;
  
  if (web_preferences.GetBoolean("plugins", &b) && b)
    command_line->AppendSwitch(switches::kEnablePlugins);
  
  if (web_preferences.GetBoolean(options::kExperimentalFeatures, &b) && b)
    command_line->AppendSwitch(
        ::switches::kEnableExperimentalWebPlatformFeatures);
  if (web_preferences.GetBoolean(options::kExperimentalCanvasFeatures, &b) && b)
    command_line->AppendSwitch(::switches::kEnableExperimentalCanvasFeatures);
  
  bool node_integration = true;
  web_preferences.GetBoolean(options::kNodeIntegration, &node_integration);
  command_line->AppendSwitchASCII(switches::kNodeIntegration,
                                  node_integration ? "true" : "false");