When Chrome hands off a URL to be opened by the external host by the ViewHost...

chrome/renderer/render_view.cc

 // Copyright (c) 2009 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 "chrome/renderer/render_view.h"
 
 #include <algorithm>
 #include <string>
 #include <vector>
 
@@ skipping 1829 matching lines @@
       last_top_level_navigation_page_id_ != page_id_ &&
       // Not interested in reloads.
       type != WebKit::WebNavigationTypeReload &&
       type != WebKit::WebNavigationTypeFormSubmitted &&
       // Must be a top level frame.
       frame->parent() == NULL) {
     // Skip if navigation is on the same page (using '#').
     GURL frame_origin = GURL(frame->url()).GetOrigin();
     if (url.GetOrigin() != frame_origin || url.ref().empty()) {
       last_top_level_navigation_page_id_ = page_id_;
-      OpenURL(url, GURL(), default_policy);
+      GURL referrer(request.httpHeaderField(WebString::fromUTF8("Referer")));
+      OpenURL(url, referrer, default_policy);
       return WebKit::WebNavigationPolicyIgnore;  // Suppress the load here.
     }
   }
 
   // A content initiated navigation may have originated from a link-click,
   // script, drag-n-drop operation, etc.
   bool is_content_initiated =
       NavigationState::FromDataSource(frame->provisionalDataSource())->
           is_content_initiated();
 
@@ skipping 1798 matching lines @@
       new PluginMsg_SignalModalDialogEvent(host_window_));
 
   message->EnableMessagePumping();  // Runs a nested message loop.
   bool rv = Send(message);
 
   PluginChannelHost::Broadcast(
       new PluginMsg_ResetModalDialogEvent(host_window_));
 
   return rv;
 }