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/browser/api/atom_api_web_contents.cc
const SkBitmap& bitmap,
                       content::ReadbackResponse response) {
  callback.Run(gfx::Image::CreateFrom1xBitmap(bitmap));
}
}  
WebContents::WebContents(v8::Isolate* isolate,
                         content::WebContents* web_contents,
                         Type type)
    : content::WebContentsObserver(web_contents),
      embedder_(nullptr),
      type_(type),
      request_id_(0),
      background_throttling_(true),
      enable_devtools_(true) {
  if (type == REMOTE) {
    web_contents->SetUserAgentOverride(GetBrowserContext()->GetUserAgent());
    Init(isolate);
    AttachAsUserData(web_contents);
  } else {
    const mate::Dictionary options = mate::Dictionary::CreateEmpty(isolate);
    auto session = Session::CreateFrom(isolate, GetBrowserContext());
    session_.Reset(isolate, session.ToV8());
    InitWithSessionAndOptions(isolate, web_contents, session, options);
  }
}
WebContents::WebContents(v8::Isolate* isolate,