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.h
}
  
  void OnCursorChange(const content::WebCursor& cursor);
  
  void OnRendererMessage(const base::string16& channel,
                         const base::ListValue& args);
  
  void OnRendererMessageSync(const base::string16& channel,
                             const base::ListValue& args,
                             IPC::Message* message);
  v8::Global<v8::Value> session_;
  v8::Global<v8::Value> devtools_web_contents_;
  v8::Global<v8::Value> debugger_;
  std::unique_ptr<WebViewGuestDelegate> guest_delegate_;
  
  WebContents* embedder_;
  
  Type type_;
  
  uint32_t request_id_;
  
  bool background_throttling_;
  
  bool enable_devtools_;
  DISALLOW_COPY_AND_ASSIGN(WebContents);
};
}  
}  
#endif