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
return GetID() == web_contents->GetID();
}
void WebContents::LoadURL(const GURL& url, const mate::Dictionary& options) {
  if (!url.is_valid()) {
    Emit("did-fail-load",
         static_cast<int>(net::ERR_INVALID_URL),
         net::ErrorToShortString(net::ERR_INVALID_URL),
         url.possibly_invalid_spec(),
         true);
    return;
  }
  content::NavigationController::LoadURLParams params(url);
  GURL http_referrer;
  if (options.Get("httpReferrer", &http_referrer))
    params.referrer = content::Referrer(http_referrer.GetAsReferrer(),
                                        blink::WebReferrerPolicyDefault);
  std::string user_agent;
  if (options.Get("userAgent", &user_agent))
    web_contents()->SetUserAgentOverride(user_agent);
  std::string extra_headers;
  if (options.Get("extraHeaders", &extra_headers))
    params.extra_headers = extra_headers;
  scoped_refptr<content::ResourceRequestBodyImpl> body;
  if (options.Get("postData", &body)) {
    params.post_data = body;
    params.load_type = content::NavigationController::LOAD_TYPE_HTTP_POST;
  }
  params.transition_type = ui::PAGE_TRANSITION_TYPED;