[ios] Show Default Browser fullscreen promo if there is no blocking UI

Bug: 1107489
Change-Id: I2604a982f3a31ed7be5d8b74eb6fe5aae2564fce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2404377
Auto-Submit: Chris Lu <thegreenfrog@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806153}

ios/chrome/browser/ui/main/default_browser_scene_agent.mm

@@ -47,7 +47,7 @@
   // SceneActivationLevelForegroundActive. Show the UI if user has met the
   // qualifications to be shown the promo.
   if (level == SceneActivationLevelForegroundActive &&
-      appState.shouldShowDefaultBrowserPromo && appState.currentUIBlocker) {
+      appState.shouldShowDefaultBrowserPromo && !appState.currentUIBlocker) {
     [HandlerForProtocol(self.dispatcher, WhatsNewCommands)
         showDefaultBrowserFullscreenPromo];
     appState.shouldShowDefaultBrowserPromo = NO;