[Tab Groups Collapse] Kinda fix tab group underline on collapsed groups.

This makes collapse looks slightly more useful. Without this the
underline make the tab group still look not collapsed.

This will need more work to spec, but thought it was a nice update.

Bug: 1018230
Change-Id: I22343f34aea7d9f42e2a1cfd8205643973e50686
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2207504
Commit-Queue: Charlene Yan <cyan@chromium.org>
Reviewed-by: Connie Wan <connily@chromium.org>
Cr-Commit-Position: refs/heads/master@{#769933}

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

@@ -46,6 +46,9 @@ void TabGroupViews::UpdateVisuals() {
 }
 
 gfx::Rect TabGroupViews::GetBounds() const {
+  if (tab_strip_->controller()->GetGroupCollapsedState(group_))
+    return header_->bounds();
+
   const Tab* last_tab = GetLastTabInGroup();
   if (!last_tab)
     return header_->bounds();