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 web_contents()->GetURL();
}
base::string16 WebContents::GetTitle() const {
  return web_contents()->GetTitle();
}
bool WebContents::IsLoading() const {
  return web_contents()->IsLoading();
}
bool WebContents::IsLoadingMainFrame() const {
  
  
  return (web_contents()->GetLastCommittedURL().is_empty() ||
          web_contents()->GetSiteInstance() !=
          web_contents()->GetPendingSiteInstance()) && IsLoading();
}
bool WebContents::IsWaitingForResponse() const {
  return web_contents()->IsWaitingForResponse();
}
void WebContents::Stop() {
  web_contents()->Stop();
}
void WebContents::GoBack() {
  atom::AtomBrowserClient::SuppressRendererProcessRestartForOnce();
  web_contents()->GetController().GoBack();
}
void WebContents::GoForward() {