[ios] Fix first run incognito issues for Multi-Windows

When Chrome is in first run state, opening a second window in
incognito, blocks the UI, and doesn't show an ntp.
Fixed by showing ntp on empty tab list (removed out-of-date comment)
Fixed by skipping first run ui on incognito.

Bug: 1113547
Change-Id: I5281acb44ea3575c157988e86b855a404488a9e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2362964Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: David Jean <djean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800934}

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

@@ -632,7 +632,8 @@ const char kMultiWindowOpenInNewWindowHistogram[] =
 
   // If this is first run, show the first run UI on top of the new tab.
   // If this isn't first run, check if the sign-in promo needs to display.
-  if (firstRun && !self.mainController.isPresentingFirstRunUI) {
+  if (firstRun && launchMode != ApplicationMode::INCOGNITO &&
+      !self.mainController.isPresentingFirstRunUI) {
     [self.mainController prepareForFirstRunUI:self.sceneState];
     [self showFirstRunUI];
     // Do not ever show the 'restore' infobar during first run.
@@ -1518,10 +1519,7 @@ const char kMultiWindowOpenInNewWindowHistogram[] =
     return YES;
   }
 
-  // If there is a URLLoading activity, avoid opening a new tab as the NTP would
-  // flash before the target URL is loaded.
-  return browser->GetWebStateList()->empty() &&
-         !(browser->GetBrowserState()->IsOffTheRecord());
+  return browser->GetWebStateList()->empty();
 }
 
 #pragma mark - SceneURLLoadingServiceDelegate