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 auto view = web_contents()->GetRenderWidgetHostView();
  if (view)
    view->EndFrameSubscription();
}
void WebContents::StartDrag(const mate::Dictionary& item,
                            mate::Arguments* args) {
  base::FilePath file;
  std::vector<base::FilePath> files;
  if (!item.Get("files", &files) && item.Get("file", &file)) {
    files.push_back(file);
  }
  mate::Handle<NativeImage> icon;
  if (!item.Get("icon", &icon) && !file.empty()) {
    
  }
  
  if (icon.IsEmpty()) {
    args->ThrowError("icon must be set");
    return;
  }
  
  if (!files.empty()) {
    base::MessageLoop::ScopedNestableTaskAllower allow(
        base::MessageLoop::current());
    DragFileItems(files, icon->image(), web_contents()->GetNativeView());
  } else {
    args->ThrowError("There is nothing to drag");
  }
}
void WebContents::CapturePage(mate::Arguments* args) {