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
content::NavigationHandle* navigation_handle) {
  bool is_main_frame = navigation_handle->IsInMainFrame();
  if (navigation_handle->HasCommitted() && !navigation_handle->IsErrorPage()) {
    auto url = navigation_handle->GetURL();
    bool is_in_page = navigation_handle->IsSamePage();
    if (is_main_frame && !is_in_page) {
      Emit("did-navigate", url);
    } else if (is_in_page) {
      Emit("did-navigate-in-page", url, is_main_frame);
    }
  } else {
    auto url = navigation_handle->GetURL();
    int code = navigation_handle->GetNetErrorCode();
    auto description = net::ErrorToShortString(code);
    Emit("did-fail-provisional-load", code, description, url, is_main_frame);
    
    if (code != net::ERR_ABORTED)
      Emit("did-fail-load", code, description, url, is_main_frame);
  }
}
void WebContents::TitleWasSet(content::NavigationEntry* entry,