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()->PasteAndMatchStyle();
}
void WebContents::Delete() {
  web_contents()->Delete();
}
void WebContents::SelectAll() {
  web_contents()->SelectAll();
}
void WebContents::Unselect() {
  web_contents()->Unselect();
}
void WebContents::Replace(const base::string16& word) {
  web_contents()->Replace(word);
}
void WebContents::ReplaceMisspelling(const base::string16& word) {
  web_contents()->ReplaceMisspelling(word);
}
uint32_t WebContents::FindInPage(mate::Arguments* args) {
  uint32_t request_id = GetNextRequestId();
  base::string16 search_text;
  blink::WebFindOptions options;
  if (!args->GetNext(&search_text) || search_text.empty()) {
    args->ThrowError("Must provide a non-empty search content");
    return 0;
  }
  args->GetNext(&options);
  web_contents()->Find(request_id, search_text, options);
  return request_id;
}
void WebContents::StopFindInPage(content::StopFindAction action) {