[Tab Groups Collapse] Update the visibility of tabs when collapsing.

This fixes the issue with the loading favicon still appearing when the
group is collapsed.

Bug: 1018230
Change-Id: Ia985cb2fa5d83fdb886a2e3004e7d44909e522e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2240450Reviewed-by: Connie Wan <connily@chromium.org>
Commit-Queue: Charlene Yan <cyan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#777538}

chrome/browser/ui/views/tabs/browser_tab_strip_controller.cc

@@ -362,6 +362,11 @@ void BrowserTabStripController::ToggleTabGroupCollapsedState(
     model_->ActivateTabAt(next_active.value(),
                           {TabStripModel::GestureType::kOther});
   }
+
+  std::vector<int> tabs_in_group = ListTabsInGroup(group);
+  for (int i : tabs_in_group)
+    tabstrip_->tab_at(i)->SetVisible(is_currently_collapsed);
+
   tab_groups::TabGroupVisualData new_data(
       GetGroupTitle(group), GetGroupColorId(group), !is_currently_collapsed);
   model_->group_model()->GetTabGroup(group)->SetVisualData(new_data, true);