Fix tab visibility when the last inactive tab is in a collapsed group.

Tab widths are cached during UpdateIdealBounds for subsequent calls
to GetActiveWidth and GetInactiveWidth. If the last inactive tab in
any invocation of UpdateIdealBounds() is in a collapsed group, its
width of kTabOverlap will end up being recorded as the inactive tab
width. This most prominently manifested as a bug in calculating tab
visibility.

Bug: 1140388
Change-Id: Ie9ecdbacf49ffdb829f1ff208d4f22e077457b94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2542769
Commit-Queue: Taylor Bergquist <tbergquist@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828414}

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

@@ -313,17 +313,8 @@ std::vector<gfx::Rect> TabStripLayoutHelper::CalculateIdealBounds(
     auto pinned = i <= last_pinned_tab_slot_index ? TabPinned::kPinned
                                                   : TabPinned::kUnpinned;
 
-    // The slot can only be collapsed if it is a tab and in a collapsed group.
-    // If the slot is indeed a tab and in a group, check the collapsed state of
-    // the group to determine if it is collapsed.
     // A collapsed tab animates close like a closed tab.
-    base::Optional<tab_groups::TabGroupId> id = slots_[i].view->group();
-    bool slot_is_collapsed_tab =
-        (slots_[i].type == ViewType::kTab && id.has_value())
-            ? controller_->IsGroupCollapsed(id.value())
-            : false;
-
-    auto open = (slots_[i].animation->IsClosing() || slot_is_collapsed_tab)
+    auto open = (slots_[i].animation->IsClosing() || SlotIsCollapsedTab(i))
                     ? TabOpen::kClosed
                     : TabOpen::kOpen;
     TabAnimationState ideal_animation_state =
@@ -448,6 +439,10 @@ TabStripLayoutHelper::GetCurrentTabWidthConstraints() const {
 void TabStripLayoutHelper::UpdateCachedTabWidth(int tab_index,
                                                 int tab_width,
                                                 bool active) {
+  // If the slot is collapsed, its width should never be reported as the
+  // current active or inactive tab width - it's not even visible.
+  if (SlotIsCollapsedTab(tab_index))
+    return;
   if (active)
     active_tab_width_ = tab_width;
   else
@@ -458,3 +453,13 @@ bool TabStripLayoutHelper::WidthsConstrainedForClosingMode() {
   return tab_width_override_.has_value() ||
          tabstrip_width_override_.has_value();
 }
+
+bool TabStripLayoutHelper::SlotIsCollapsedTab(int i) const {
+  // The slot can only be collapsed if it is a tab and in a collapsed group.
+  // If the slot is indeed a tab and in a group, check the collapsed state of
+  // the group to determine if it is collapsed.
+  const base::Optional<tab_groups::TabGroupId> id = slots_[i].view->group();
+  return (slots_[i].type == ViewType::kTab && id.has_value())
+             ? controller_->IsGroupCollapsed(id.value())
+             : false;
+}

chrome/browser/ui/views/tabs/tab_strip_layout_helper.h

@@ -171,6 +171,9 @@ class TabStripLayoutHelper {
   // Returns true if any width constraint is currently being enforced.
   bool WidthsConstrainedForClosingMode();
 
+  // True iff the slot at index |i| is a tab that is in a collapsed group.
+  bool SlotIsCollapsedTab(int i) const;
+
   // The owning tabstrip's controller.
   const TabStripController* const controller_;