Fix HighlightCloseButton crash....

chrome/browser/views/tabs/tab_strip.cc

 // Copyright (c) 2010 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/views/tabs/tab_strip.h"
 
 #include "app/animation_container.h"
 #include "app/drag_drop_types.h"
 #include "app/l10n_util.h"
 #include "app/os_exchange_data.h"
@@ skipping 191 matching lines @@
   // the mouse is currently over to show the "hot" state of the close button.
   void HighlightCloseButton() {
     if (tabstrip_->available_width_for_tabs_ == -1 ||
         tabstrip_->IsDragSessionActive()) {
       // This function is not required (and indeed may crash!) for removes
       // spawned by non-mouse closes and drag-detaches.
       return;
     }
 
 #if defined(OS_WIN)
+    views::Widget* widget = tabstrip_->GetWidget();
+    // This can be null during shutdown. See http://crbug.com/42737.
+    if (!widget)
+      return;
     // Force the close button (that slides under the mouse) to highlight by
     // saying the mouse just moved, but sending the same coordinates.
     DWORD pos = GetMessagePos();
     POINT cursor_point = {GET_X_LPARAM(pos), GET_Y_LPARAM(pos)};
-    views::Widget* widget = tabstrip_->GetWidget();
     MapWindowPoints(NULL, widget->GetNativeView(), &cursor_point, 1);
 
     static_cast<views::WidgetWin*>(widget)->ResetLastMouseMoveFlag();
     // Return to message loop - otherwise we may disrupt some operation that's
     // in progress.
     SendMessage(widget->GetNativeView(), WM_MOUSEMOVE, 0,
                 MAKELPARAM(cursor_point.x, cursor_point.y));
 #else
     NOTIMPLEMENTED();
 #endif
@@ skipping 1556 matching lines @@
   return tab_data_.size();
 }
 
 int TabStrip::TabDataIndexOfTab(Tab* tab) const {
   for (size_t i = 0; i < tab_data_.size(); ++i) {
     if (tab_data_[i].tab == tab)
       return i;
   }
   return -1;
 }