Fix #8661: Always allow WebKit to load popup URLs before switching tabs

Sources/Brave/Frontend/Browser/BrowserViewController/BVC+WKNavigationDelegate.swift

@@ -1016,6 +1016,16 @@ extension BrowserViewController: WKUIDelegate {
     newTab.url = URL(string: "about:blank")
 
     toolbarVisibilityViewModel.toolbarState = .expanded
+
+    // Wait until WebKit starts the request before selecting the new tab, otherwise the tab manager may
+    // restore it as if it was a dead tab.
+    var observation: NSKeyValueObservation?
+    observation = newTab.webView?.observe(\.url, changeHandler: { [weak self] webView, _ in
+      _ = observation // Silence write but not read warning
+      observation = nil
+      guard let self = self, let tab = self.tabManager[webView] else { return }
+      self.tabManager.selectTab(tab)
+    })
 
     return newTab.webView
   }

Sources/Brave/Frontend/Browser/TabManager.swift

@@ -411,14 +411,6 @@ class TabManager: NSObject {
   @MainActor func addPopupForParentTab(_ parentTab: Tab, configuration: WKWebViewConfiguration) -> Tab {
     let popup = Tab(configuration: configuration, id: UUID(), type: parentTab.type, tabGeneratorAPI: tabGeneratorAPI)
     configureTab(popup, request: nil, afterTab: parentTab, flushToDisk: true, zombie: false, isPopup: true)
-
-    // Wait momentarily before selecting the new tab, otherwise the parent tab
-    // may be unable to set `window.location` on the popup immediately after
-    // calling `window.open("")`.
-    DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(100)) {
-      self.selectTab(popup)
-    }
-
     return popup
   }