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("devtools-reload-page");
}
void WebContents::DevToolsFocused() {
  Emit("devtools-focused");
}
void WebContents::DevToolsOpened() {
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  auto handle = WebContents::CreateFrom(
      isolate(), managed_web_contents()->GetDevToolsWebContents());
  devtools_web_contents_.Reset(isolate(), handle.ToV8());
  
  base::FundamentalValue tab_id(ID());
  managed_web_contents()->CallClientFunction(
      "DevToolsAPI.setInspectedTabId", &tab_id, nullptr, nullptr);
  
  if (owner_window())
    handle->SetOwnerWindow(managed_web_contents()->GetDevToolsWebContents(),
                           owner_window());
  Emit("devtools-opened");
}
void WebContents::DevToolsClosed() {