Overlay browser view not shown when using CefWindow::AddOverlayView

[Taronyu]

Describe the bug
We use AddOverlayView with browser views to embed a browser view on top of our main browser. Starting from CEF 125 this was broken due to a crash (issue #3784) which got fixed thankfully. However, now the browser view is not shown anymore. In our application I see that the browser instance is null. According to the documentation the browser is only created once the view is added to the view hierarchy, but as far as I understood this should happen when CefWindow::AddOverlayView is called.

I did not see anything obviously wrong with the calling code. I compared it to other elements of cefclient and cefsimple that are added via AddOverlayView. I suspect that the browser instance is not created, given that CefBrowserView::GetBrowser returns nullptr.

To Reproduce
Steps to reproduce the behavior:

1. Apply provided patch file to cefclient
2. Build cefclient
3. Launch cefclient with --use-views --hide-frame --hide-controls
4. Only the main website is shown, not the overlay view pointing to https://bitbucket.org/chromiumembedded/cef/

Expected behavior
Browser view is created and shown in parent window on top of its content.

Screenshots
N/A

Versions (please complete the following information):

• OS: Windows 11
• CEF Version: master (build tag 129.0.0-master.3051+g6459917+chromium-129.0.6668.0)

Additional context
With the provided patch for cefclient it is possible to reproduce the issue.
cefclient_testcode.patch

[magreenblatt]

Part of resolving this issue would be adding test coverage for mixing Alloy- and Chrome-style BrowserViews in a single Chrome-style Window. See here for background.

// [...] Alloy style Windows with the
/// Views framework can host only Alloy style BrowserViews but Chrome style
/// Windows can host both style BrowserViews. Additionally, a Chrome style
/// Window can host at most one Chrome style BrowserView but potentially
/// multiple Alloy style BrowserViews.

[magreenblatt]

@Taronyu With your use case, is the overlay BrowserView always focusable/activatable? For context, a |can_activate| argument was recently added to CefWindow::AddOverlayView (see PR #676).

[Taronyu]

Yes it is. We use it to embed a browser into a main browser window and it must be usable as a regular browser, e.g. receive keyboard and mouse input events. That PR is actually from me. Best, Philipp