Fixes possible crash in tab dragging

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

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/views/tabs/tab_drag_controller.h"
 
 #include <math.h>
 #include <set>
 
 #include "base/auto_reset.h"
@@ skipping 1411 matching lines @@
 
   // If we've removed the last Tab from the TabStrip, hide the frame now.
   if (!attached_model->empty()) {
     if (!selection_model_before_attach_.empty() &&
         selection_model_before_attach_.active() >= 0 &&
         selection_model_before_attach_.active() < attached_model->count()) {
       // Restore the selection.
       attached_model->SetSelectionFromModel(selection_model_before_attach_);
     } else if (attached_tabstrip_ == source_tabstrip_ &&
                !initial_selection_model_.empty()) {
-      // First time detaching from the source tabstrip. Reset selection model to
-      // initial_selection_model_. Before resetting though we have to remove all
-      // the tabs from initial_selection_model_ as it was created with the tabs
-      // still there.
-      ui::ListSelectionModel selection_model;
-      selection_model.Copy(initial_selection_model_);
-      for (DragData::const_reverse_iterator i(drag_data_.rbegin());
-           i != drag_data_.rend(); ++i) {
-        selection_model.DecrementFrom(i->source_model_index);
-      }
-      // We may have cleared out the selection model. Only reset it if it
-      // contains something.
-      if (!selection_model.empty())
-        attached_model->SetSelectionFromModel(selection_model);
+      RestoreInitialSelection();
     }
   }
 
   // Create the dragged view.
   if (!detach_into_browser_)
     CreateDraggedView(tab_data, drag_bounds);
 
   attached_tabstrip_->DraggedTabsDetached();
   attached_tabstrip_ = NULL;
 }
@@ skipping 418 matching lines @@
         has_one_valid_tab = true;
       }
     }
   }
   if (!has_one_valid_tab)
     return;
 
   model->SetSelectionFromModel(selection_model);
 }
 
+void TabDragController::RestoreInitialSelection() {
+  // First time detaching from the source tabstrip. Reset selection model to
+  // initial_selection_model_. Before resetting though we have to remove all
+  // the tabs from initial_selection_model_ as it was created with the tabs
+  // still there.
+  ui::ListSelectionModel selection_model;
+  selection_model.Copy(initial_selection_model_);
+  for (DragData::const_reverse_iterator i(drag_data_.rbegin());
+       i != drag_data_.rend(); ++i) {
+    selection_model.DecrementFrom(i->source_model_index);
+  }
+  // We may have cleared out the selection model. Only reset it if it
+  // contains something.
+  if (selection_model.empty())
+    return;
+
+  // The anchor/active may have been among the tabs that were dragged out. Force
+  // the anchor/active to be valid.
+  if (selection_model.anchor() == ui::ListSelectionModel::kUnselectedIndex)
+    selection_model.set_anchor(selection_model.selected_indices()[0]);
+  if (selection_model.active() == ui::ListSelectionModel::kUnselectedIndex)
+    selection_model.set_active(selection_model.selected_indices()[0]);
+  GetModel(source_tabstrip_)->SetSelectionFromModel(selection_model);
+}
+
 void TabDragController::RevertDragAt(size_t drag_index) {
   DCHECK(started_drag_);
   DCHECK(source_tabstrip_);
 
   base::AutoReset<bool> setter(&is_mutating_, true);
   TabDragData* data = &(drag_data_[drag_index]);
   if (attached_tabstrip_) {
     int index =
         GetModel(attached_tabstrip_)->GetIndexOfWebContents(data->contents);
     if (attached_tabstrip_ != source_tabstrip_) {
@@ skipping 437 matching lines @@
 gfx::Vector2d TabDragController::GetWindowOffset(
     const gfx::Point& point_in_screen) {
   TabStrip* owning_tabstrip = (attached_tabstrip_ && detach_into_browser_) ?
       attached_tabstrip_ : source_tabstrip_;
   views::View* toplevel_view = owning_tabstrip->GetWidget()->GetContentsView();
 
   gfx::Point point = point_in_screen;
   views::View::ConvertPointFromScreen(toplevel_view, &point);
   return point.OffsetFromOrigin();
 }