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
web_contents()->SetAudioMuted(muted);
}
bool WebContents::IsAudioMuted() {
  return web_contents()->IsAudioMuted();
}
void WebContents::Print(mate::Arguments* args) {
  PrintSettings settings = { false, false };
  if (args->Length() == 1 && !args->GetNext(&settings)) {
    args->ThrowError();
    return;
  }
  printing::PrintViewManagerBasic::FromWebContents(web_contents())->
      PrintNow(settings.silent, settings.print_background);
}
void WebContents::PrintToPDF(const base::DictionaryValue& setting,
                             const PrintToPDFCallback& callback) {
  printing::PrintPreviewMessageHandler::FromWebContents(web_contents())->
      PrintToPDF(setting, callback);
}
void WebContents::AddWorkSpace(mate::Arguments* args,
                               const base::FilePath& path) {
  if (path.empty()) {
    args->ThrowError("path cannot be empty");
    return;
  }
  DevToolsAddFileSystem(path);
}
void WebContents::RemoveWorkSpace(mate::Arguments* args,