Fix HighlightCloseButton crash....

chrome/browser/views/tabs/tab_strip.cc

Index: chrome/browser/views/tabs/tab_strip.cc
===================================================================
--- chrome/browser/views/tabs/tab_strip.cc	(revision 45664)
+++ chrome/browser/views/tabs/tab_strip.cc	(working copy)
@@ -209,11 +209,14 @@
     }
 
 #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();