MD History: Enable by default

chrome/browser/ui/webui/md_history_ui.h

 // Copyright 2015 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.
 
 #ifndef CHROME_BROWSER_UI_WEBUI_MD_HISTORY_UI_H_
 #define CHROME_BROWSER_UI_WEBUI_MD_HISTORY_UI_H_
 
 #include "base/macros.h"
 #include "content/public/browser/web_ui_controller.h"
 #include "ui/base/layout.h"
 
 class Profile;
 
 namespace base {
 class RefCountedMemory;
 }
 
 class MdHistoryUI : public content::WebUIController {
  public:
   explicit MdHistoryUI(content::WebUI* web_ui);
   ~MdHistoryUI() override;
 
   static bool IsEnabled(Profile* profile);
+  // Reset the current list of features and explicitly disable MD History.
+  static void DisableForTesting();
 
   static base::RefCountedMemory* GetFaviconResourceBytes(
       ui::ScaleFactor scale_factor);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MdHistoryUI);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_MD_HISTORY_UI_H_