Fix a crash which occurs while dragging tabs back to the window where they originated from.

ui/views/controls/webview/webview.cc

Index: ui/views/controls/webview/webview.cc
diff --git a/ui/views/controls/webview/webview.cc b/ui/views/controls/webview/webview.cc
index e7885005272b60c12fd514ee434102bb64d7c9ba..23cea821b056137b2c9d0fcefb74c0909e05f1b7 100644
--- a/ui/views/controls/webview/webview.cc
+++ b/ui/views/controls/webview/webview.cc
@@ -303,13 +303,13 @@ void WebView::AttachWebContents() {
   if (holder_->native_view() == view_to_attach)
     return;
 
+  holder_->Attach(view_to_attach);
+
   // Fullscreen widgets are not parented by a WebContentsView. Their visibility
   // is controlled by content i.e. (RenderWidgetHost)
   if (!is_embedding_fullscreen_widget_)
     view_to_attach->Show();
 
-  holder_->Attach(view_to_attach);
-
   // The view will not be focused automatically when it is attached, so we need
   // to pass on focus to it if the FocusManager thinks the view is focused. Note
   // that not every Widget has a focus manager.