[ios] Fix NTP landscape omnibox with alternate search engine.

Followup to crbug.com/848762, which had too broad of a fix.

This narrows the scope of the fix to RxR size class only.

Bug: 848762, 868945
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ic72760d395eea7aadc32560133c0885657852bcc
Reviewed-on: https://chromium-review.googlesource.com/1183561Reviewed-by: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584951}

ios/chrome/browser/ui/content_suggestions/content_suggestions_header_view_controller.mm

@@ -157,9 +157,10 @@ const UIEdgeInsets kSearchBoxStretchInsets = {3, 3, 3, 3};
                     safeAreaInsets:(UIEdgeInsets)safeAreaInsets {
   if (self.isShowing && IsUIRefreshPhase1Enabled()) {
     CGFloat progress =
-        self.logoIsShowing
+        self.logoIsShowing || !content_suggestions::IsRegularXRegularSizeClass()
             ? [self.headerView searchFieldProgressForOffset:offset
                                              safeAreaInsets:safeAreaInsets]
+            // RxR with no logo hides the fakebox, so always show the omnibox.
             : 1;
     if (!IsSplitToolbarMode()) {
       [self.toolbarDelegate setScrollProgressForTabletOmnibox:progress];