Fix regression in tab dragging

Introduced here: https://chromium-review.googlesource.com/c/chromium/src/+/1866058/16/chrome/browser/ui/views/tabs/tab_strip.cc#683

Not sure how to regression test this given that it's a visual/animation issue. Suggestions welcome!

Bug: 1021582
Change-Id: Ie57d4b767b84e6b3a975841538e1eb54e1037d66
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900206
Commit-Queue: Connie Wan <connily@chromium.org>
Reviewed-by: Charlene Yan <cyan@chromium.org>
Reviewed-by: Taylor Bergquist <tbergquist@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712842}

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

@@ -680,9 +680,6 @@ class TabStrip::TabDragContextImpl : public TabDragContext {
     // Let the controller know that the user stopped dragging tabs.
     tab_strip_->controller_->OnStoppedDragging();
 
-    for (size_t i = 0; i < views.size(); ++i)
-      views[i]->set_dragging(false);
-
     SetNewTabButtonVisible(true);
     if (move_only && tab_strip_->touch_layout_) {
       if (completed)
@@ -2641,6 +2638,14 @@ void TabStrip::OnGroupCloseAnimationCompleted(TabGroupId group) {
 void TabStrip::StoppedDraggingView(TabSlotView* view, bool* is_first_view) {
   int tab_data_index = GetModelIndexOf(view);
   if (tab_data_index == -1) {
+    // Ensure the drag status is updated even if the view is not a valid tab.
+    // This is primarily to make sure group headers are updated correctly.
+    // Otherwise, tab drag status is only updated in PrepareForAnimation().
+    // TODO(crbug.com/1021689): Incorporate group headers in the normal
+    // animation flow instead of handling it here and then ignoring it.
+    if (view)
+      view->set_dragging(false);
+
     // The tab was removed before the drag completed. Don't do anything.
     return;
   }

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

@@ -481,8 +481,8 @@ class TabStrip : public views::AccessiblePaneView,
   // from the tab animation code and is not a general-purpose method.
   void OnGroupCloseAnimationCompleted(TabGroupId group);
 
-  // Invoked from StoppedDraggingTabs to cleanup |tab|. If |tab| is known
-  // |is_first_tab| is set to true.
+  // Invoked from StoppedDraggingTabs to cleanup |view|. If |view| is known
+  // |is_first_view| is set to true.
   void StoppedDraggingView(TabSlotView* view, bool* is_first_view);
 
   // Invoked when a mouse event occurs over |source|. Potentially switches the