RenderWidget popup should be a NSWindow so it can go outside the main window.

content/browser/web_contents/web_contents_impl.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 "content/browser/web_contents/web_contents_impl.h"
 
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
@@ skipping 1430 matching lines @@
   if (delegate_)
     delegate_->RenderWidgetShowing();
 
   RenderWidgetHostViewPort* widget_host_view =
       RenderWidgetHostViewPort::FromRWHV(GetCreatedWidget(route_id));
   if (!widget_host_view)
     return;
   if (is_fullscreen) {
     widget_host_view->InitAsFullscreen(GetRenderWidgetHostView());
   } else {
-    widget_host_view->InitAsPopup(GetRenderWidgetHostView(), initial_pos);
+    WebContentsViewDelegate* delegate =
+        GetContentClient()->browser()->GetWebContentsViewDelegate(this);
+    widget_host_view->InitAsPopup(GetRenderWidgetHostView(),
+                                  initial_pos, delegate);
   }
 
   RenderWidgetHostImpl* render_widget_host_impl =
       RenderWidgetHostImpl::From(widget_host_view->GetRenderWidgetHost());
   render_widget_host_impl->Init();
   // Only allow privileged mouse lock for fullscreen render widget, which is
   // used to implement Pepper Flash fullscreen.
   render_widget_host_impl->set_allow_privileged_mouse_lock(is_fullscreen);
 
 #if defined(OS_MACOSX)
@@ skipping 1931 matching lines @@
 
 BrowserPluginGuest* WebContentsImpl::GetBrowserPluginGuest() {
   return browser_plugin_guest_.get();
 }
 
 BrowserPluginEmbedder* WebContentsImpl::GetBrowserPluginEmbedder() {
   return browser_plugin_embedder_.get();
 }
 
 }  // namespace content