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

ui/views/controls/webview/webview.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 "ui/views/controls/webview/webview.h"
 
 #include "content/public/browser/browser_accessibility_state.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/navigation_controller.h"
 #include "content/public/browser/render_view_host.h"
@@ skipping 285 matching lines @@
   if (!GetWidget() || !web_contents())
     return;
 
   const gfx::NativeView view_to_attach = is_embedding_fullscreen_widget_ ?
       web_contents()->GetFullscreenRenderWidgetHostView()->GetNativeView() :
       web_contents()->GetNativeView();
   OnBoundsChanged(bounds());
   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.
   FocusManager* const focus_manager = GetFocusManager();
   if (focus_manager && focus_manager->GetFocusedView() == this)
     OnFocus();
 
 #if defined(OS_WIN)
   if (!is_embedding_fullscreen_widget_) {
     web_contents()->SetParentNativeViewAccessible(
@@ skipping 54 matching lines @@
   if (!contents) {
     content::WebContents::CreateParams create_params(
         browser_context, NULL);
     return content::WebContents::Create(create_params);
   }
 
   return contents;
 }
 
 }  // namespace views