Fixing browser crash in the linux tab dragging code.

chrome/browser/ui/gtk/tabs/drag_data.cc

 // Copyright (c) 2011 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/gtk/tabs/drag_data.h"
 
 #include "chrome/browser/tabs/tab_strip_model.h"
 #include "chrome/browser/ui/gtk/tabs/tab_gtk.h"
 #include "chrome/browser/ui/tab_contents/tab_contents_wrapper.h"
 #include "content/browser/tab_contents/tab_contents.h"
@@ skipping 80 matching lines @@
   if (static_cast<int>(index) == source_tab_index_)
     add_types |= TabStripModel::ADD_ACTIVE;
   return add_types;
 }
 
 TabContentsWrapper* DragData::GetSourceTabContentsWrapper() {
   return GetSourceTabData()->contents_;
 }
 
 TabContents* DragData::GetSourceTabContents() {
-  return GetSourceTabData()->contents_->tab_contents();
+  TabContentsWrapper* contents = GetSourceTabData()->contents_;
+  return contents ? contents->tab_contents(): NULL;
 }
 
 DraggedTabData* DragData::GetSourceTabData() {
   return get(source_tab_index_);
 }