[iOS][Getaway] Disable side swipe when the blocker is shown.

Disables the side swipes in BVC when the blocking UI is displayed.

Bug: none
Change-Id: Iff04be46bc078b2f523406770b757702732b8ced
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2592798
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Auto-Submit: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#838146}

ios/chrome/browser/ui/browser_view/browser_view_controller.mm

@@ -4874,6 +4874,11 @@ NSString* const kBrowserViewControllerSnackbarCategory =
   if (!self.active)
     return YES;
 
+  BOOL isShowingIncognitoBlocker = (self.blockingView.superview != nil);
+  if (isShowingIncognitoBlocker) {
+    return YES;
+  }
+
   return NO;
 }