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 1340 matching lines @@
     // enough to trigger a drag.
     if (started_drag_) {
       RestoreFocus();
       if (type == CANCELED)
         RevertDrag();
       else
         CompleteDrag();
     }
   } else if (drag_data_.size() > 1) {
     initial_selection_model_.Clear();
-    RevertDrag();
+    if (started_drag_)
+      RevertDrag();
   }  // else case the only tab we were dragging was deleted. Nothing to do.
 
   // Clear out drag data so we don't attempt to do anything with it.
   drag_data_.clear();
 
   TabStrip* owning_tabstrip = attached_tabstrip_ ?
       attached_tabstrip_ : source_tabstrip_;
   owning_tabstrip->DestroyDragController();
 }
 
@@ skipping 413 matching lines @@
        it != browser_list->end(); ++it) {
     if ((*it)->tab_strip_model()->empty())
       exclude.insert((*it)->window()->GetNativeWindow());
   }
 #endif
   return GetLocalProcessWindowAtPoint(host_desktop_type_,
                                       screen_point,
                                       exclude);
 
 }