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
Emit("did-start-loading");
}
void WebContents::DidStopLoading() {
  Emit("did-stop-loading");
}
void WebContents::DidGetResourceResponseStart(
    const content::ResourceRequestDetails& details) {
  Emit("did-get-response-details",
       details.socket_address.IsEmpty(),
       details.url,
       details.original_url,
       details.http_response_code,
       details.method,
       details.referrer,
       details.headers.get(),
       ResourceTypeToString(details.resource_type));
}
void WebContents::DidGetRedirectForResourceRequest(
    content::RenderFrameHost* render_frame_host,
    const content::ResourceRedirectDetails& details) {
  Emit("did-get-redirect-request",
       details.url,
       details.new_url,
       (details.resource_type == content::RESOURCE_TYPE_MAIN_FRAME),
       details.http_response_code,
       details.method,
       details.referrer,
       details.headers.get());
}
void WebContents::DidFinishNavigation(