Embedding arbitrary web content is problematic when it comes to keyboard shortcuts because:
- Web content can steal app shortcuts (see e.g. brave/browser-laptop#4407)
- Blocked web content (e.g. a focused `<webview>` performing expensive computation) will also prevent app shortcuts from firing immediately

To fix this, we need a way to _always_ handle certain shortcuts in the main process. I think the most flexible solution would be something like this:

``` js
app.addProtectedShortcut('CmdOrCtrl+Tab', (event) => {
  event.preventDefault();
});
```

We could then implement:

``` cpp
bool CommonWebContentsDelegate::PreHandleKeyboardEvent(
    content::WebContents* source,
    const content::NativeWebKeyboardEvent& event,
    bool* is_keyboard_shortcut) {
  return /* event is protected shortcut and the handler called preventDefault */;
}
```

@zcbenz Thoughts? I'm happy to work on this if we come up with a reasonable approach.

atom/common/native_mate_converters/blink_converter.cc
v8::Isolate* isolate,
    const blink::WebCache::ResourceTypeStat& stat) {
  mate::Dictionary dict = mate::Dictionary::CreateEmpty(isolate);
  dict.Set("count", static_cast<uint32_t>(stat.count));
  dict.Set("size", static_cast<double>(stat.size));
  dict.Set("liveSize", static_cast<double>(stat.liveSize));
  dict.Set("decodedSize", static_cast<double>(stat.decodedSize));
  dict.Set("purgedSize", static_cast<double>(stat.purgedSize));
  dict.Set("purgeableSize", static_cast<double>(stat.purgeableSize));
  return dict.GetHandle();
}
v8::Local<v8::Value> Converter<blink::WebCache::ResourceTypeStats>::ToV8(
    v8::Isolate* isolate,
    const blink::WebCache::ResourceTypeStats& stats) {
  mate::Dictionary dict = mate::Dictionary::CreateEmpty(isolate);
  dict.Set("images", stats.images);
  dict.Set("scripts", stats.scripts);
  dict.Set("cssStyleSheets", stats.cssStyleSheets);
  dict.Set("xslStyleSheets", stats.xslStyleSheets);
  dict.Set("fonts", stats.fonts);
  dict.Set("other", stats.other);
  return dict.GetHandle();
}
}