[ios] Fix NTP scrolled omnibox for iOS10.

This was broken by crrev.com/548047, which should have been wrapped in a ui
refresh flag.

Bug: 819460, 831555
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I4b081548de5f058a81530d9dd20f369e2e1fca7d
Reviewed-on: https://chromium-review.googlesource.com/1008044Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549942}

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

@@ -92,10 +92,12 @@ layoutAttributesForSupplementaryViewOfKind:(NSString*)kind
 
     // Prevent the fake omnibox from scrolling up off of the screen.
     CGFloat topSafeArea = 0;
-    if (@available(iOS 11, *)) {
-      topSafeArea = self.collectionView.safeAreaInsets.top;
-    } else {
-      topSafeArea = StatusBarHeight();
+    if (IsUIRefreshPhase1Enabled()) {
+      if (@available(iOS 11, *)) {
+        topSafeArea = self.collectionView.safeAreaInsets.top;
+      } else {
+        topSafeArea = StatusBarHeight();
+      }
     }
     CGFloat minY = headerHeight - ntp_header::kMinHeaderHeight - topSafeArea;
     if (contentOffset.y > minY)