Makes a handful of DataSources not replace the existing

chrome/browser/dom_ui/new_tab_ui.cc

 // Copyright (c) 2011 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 "build/build_config.h"
 
 #include "chrome/browser/dom_ui/new_tab_ui.h"
 
 #include <set>
 
@@ skipping 580 matching lines @@
 
   scoped_refptr<RefCountedBytes> html_bytes(
       profile_->GetNTPResourceCache()->GetNewTabHTML(is_off_the_record));
 
   SendResponse(request_id, html_bytes);
 }
 
 std::string NewTabUI::NewTabHTMLSource::GetMimeType(const std::string&) const {
   return "text/html";
 }
+
+bool NewTabUI::NewTabHTMLSource::ShouldReplaceExistingSource() const {
+  return false;
+}