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 f1f12d015446d245c42fea9bac362d5627040814..7e31097059dd5156f9d2ad00328137c46d701324 100644
--- a/ui/views/controls/webview/webview.cc
+++ b/ui/views/controls/webview/webview.cc
@@ -303,13 +303,14 @@ void WebView::AttachWebContents() {
   if (holder_->native_view() == view_to_attach)
     return;
 
+  // The WCV needs to be parented before making it visible.
+  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.