Don't crash DRT if dumpFilenameBeingDragged() is called outside a drag.

content/shell/renderer/test_runner/event_sender.cc

Index: content/shell/renderer/test_runner/event_sender.cc
diff --git a/content/shell/renderer/test_runner/event_sender.cc b/content/shell/renderer/test_runner/event_sender.cc
index 4d1461b43b5047d896e5b683688c9adc6fe6a0a4..e7a3e23c714c86e201549af8477e284914717605 100644
--- a/content/shell/renderer/test_runner/event_sender.cc
+++ b/content/shell/renderer/test_runner/event_sender.cc
@@ -1559,6 +1559,9 @@ void EventSender::SetTouchCancelable(bool cancelable) {
 }
 
 void EventSender::DumpFilenameBeingDragged() {
+  if (current_drag_data_.isNull())
+    return;
+
   WebString filename;
   WebVector<WebDragData::Item> items = current_drag_data_.items();
   for (size_t i = 0; i < items.size(); ++i) {