Fix another d&d crash that happens when the tab contents

webkit/glue/webview_impl.cc

 /*
 * Copyright 2007 Google Inc. All Rights Reserved.
 *
 * Portions Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
 *
 * ***** BEGIN LICENSE BLOCK *****
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
@@ skipping 1570 matching lines @@
     const WebPoint& client_point,
     const WebPoint& screen_point) {
   PlatformMouseEvent pme(webkit_glue::WebPointToIntPoint(client_point),
                          webkit_glue::WebPointToIntPoint(screen_point),
                          LeftButton, MouseEventMoved, 0, false, false, false,
                          false, 0);
   page_->mainFrame()->eventHandler()->dragSourceMovedTo(pme);
 }
 
 void WebViewImpl::DragSourceSystemDragEnded() {
-  page_->dragController()->dragEnded();
-  DCHECK(doing_drag_and_drop_);
-  doing_drag_and_drop_ = false;
+  // It's possible for us to get this callback while not doing a drag if
+  // it's from a previous page that got unloaded.
+  if (doing_drag_and_drop_) {
+    page_->dragController()->dragEnded();
+    doing_drag_and_drop_ = false;
+  }
 }
 
 bool WebViewImpl::DragTargetDragEnter(
     const WebDragData& web_drag_data,
     int identity,
     const WebPoint& client_point,
     const WebPoint& screen_point) {
   DCHECK(!current_drag_data_.get());
 
   current_drag_data_ =
@@ skipping 295 matching lines @@
 
   return document->focusedNode();
 }
 
 HitTestResult WebViewImpl::HitTestResultForWindowPos(const IntPoint& pos) {
   IntPoint doc_point(
       page_->mainFrame()->view()->windowToContents(pos));
   return page_->mainFrame()->eventHandler()->
       hitTestResultAtPoint(doc_point, false);
 }