When I load PHPMyAdmin, it uses a frameset with a database list on the left and menu and content on the right. The menu in the right frame at the top is in a fixed position div. When I first open PHPMyAdmin the menu is there, but once I click on databases in the left frame, the right frame loads a new page and the fixed position div no longer displays. The white block of space also scrolls with the page so it's not even fixed positioned. If I open Web Inspector and turn off the css for positon: fixed;, the menu then appears and I can toggle fixed back on, causing it to work as expected and it remains until I load new content into the frame and then it's gone again. If I load the right frame pages into a new tab or window, the fixed div appears fine. It's only when loading into a frameset that the problem is occurring.
Confirmed with <http://demo.phpmyadmin.net/STABLE/> (login:root, empty password). I'm getting a blank menu bar even on initial load.
Tried to regress this but demo.phpmyadmin.net is way too slow.
This is the only likely cause in that range: http://trac.webkit.org/changeset/139461
Verified on Chromium ToT with "--enable-fixed-position-creates-stacking-context --enable-fixed-position-compositing".
Just tested without http://trac.webkit.org/changeset/139461 and the bug still existed, so this seems not a recent regression.
When a non-compositing page contains some not-composited fixed position element because of bounds out-of-view, when the element changes position and RenderLayerCompositor::updateCompositingLayers() is called, the function may return early because of "if (!m_reevaluateCompositingAfterLayout && !m_compositing)" without updating the compositing layers.
Should set m_reevaluateCompositingAfterLayout when a fixed position element is not composited because of bounds out-of-view.
Created attachment 184286 [details]
Comment on attachment 184286 [details]
Sorry for the wrong version of the expected file.
Created attachment 184301 [details]
Comment on attachment 184301 [details]
Clearing flags on attachment: 184301
Committed r140593: <http://trac.webkit.org/changeset/140593>
All reviewed patches have been landed. Closing bug.