Revert "[ios] Fix test ReplaceScrolledOffScreenCell"

This reverts commit bb4205e3.

Reason for revert: this test still fails. example: https://ci.chromium.org/p/chrome/builders/ci/ipad-device/13104

Original change's description:
> [ios] Fix test ReplaceScrolledOffScreenCell
>
> Re-enables disabled test ReplaceScrolledOffScreenCell.
> Uses hardcoded number of items in test instead of flakey
> dynamic approach.
>
> Bug: 1104872
> Change-Id: Ic7ca34b7fa8936452fbc6efaee12563803eb023e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2450812
> Reviewed-by: Mark Cogan <marq@chromium.org>
> Commit-Queue: edchin <edchin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#814776}

TBR=marq@chromium.org,edchin@chromium.org

Change-Id: I01adfe29516ad5d31642892331f573c96246b1dd
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1104872
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2461110Reviewed-by: Stepan Khapugin <stkhapugin@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815101}

ios/chrome/browser/ui/tab_grid/grid/grid_view_controller_unittest.mm

@@ -183,7 +183,14 @@ TEST_F(GridViewControllerTest, MoveUnselectedItem) {
 
 // Tests that |-replaceItemID:withItem:| does not crash when updating an item
 // that is scrolled offscreen.
-TEST_F(GridViewControllerTest, ReplaceScrolledOffScreenCell) {
+TEST_F(GridViewControllerTest, DISABLED_ReplaceScrolledOffScreenCell) {
+  // TODO(crbug.com/1104872): On iOS 14 iPhone X, visibleCellsCount is always
+  // equal to the total number of cells, so the while loop below never
+  // terminates.
+  if (@available(iOS 14, *)) {
+    return;
+  }
+
   // This test requires that the collection view be placed on the screen.
   SetRootViewController(view_controller_);
   EXPECT_TRUE(base::test::ios::WaitUntilConditionOrTimeout(
@@ -191,16 +198,17 @@ TEST_F(GridViewControllerTest, ReplaceScrolledOffScreenCell) {
         return view_controller_.collectionView.visibleCells.count > 0;
       }));
   NSArray* items = view_controller_.items;
-  // Keep adding items until we get an item that is offscreen.
-  // TODO(crbug.com/1104872): Since device sizes may vary, it would be better to
-  // not use a fixed number of items. But that approach (using the count of
-  // visibleCells) was flakey. 30 items should be plenty to produce offscreen
-  // items even on and iPad.
-  while (items.count <= 30) {
+  // Keep adding items until we get an item that is offscreen. Since device
+  // sizes may vary, this is better than creating a fixed number of items that
+  // we think will overflow to offscreen items.
+  NSUInteger visibleCellsCount =
+      view_controller_.collectionView.visibleCells.count;
+  while (visibleCellsCount >= items.count) {
     NSString* uniqueID =
         [NSString stringWithFormat:@"%d", base::checked_cast<int>(items.count)];
     GridItem* item = [[GridItem alloc] initWithIdentifier:uniqueID];
     [view_controller_ insertItem:item atIndex:0 selectedItemID:@"A"];
+    visibleCellsCount = view_controller_.collectionView.visibleCells.count;
   }
   // The last item ("B") is scrolled off screen.
   GridItem* item = [[GridItem alloc] initWithIdentifier:@"NEW-ITEM"];