Enable Material Design downloads on Canary/Chromium

chrome/browser/ui/webui/downloads_ui_browsertest.h

 // Copyright 2013 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_DOWNLOADS_UI_BROWSERTEST_H_
 #define CHROME_BROWSER_UI_WEBUI_DOWNLOADS_UI_BROWSERTEST_H_
 
 #include "chrome/test/base/web_ui_browser_test.h"
 
 // This is a helper class used by downloads_ui_browsertest.js.
 class DownloadsUIBrowserTest : public WebUIBrowserTest {
  public:
   DownloadsUIBrowserTest();
   ~DownloadsUIBrowserTest() override;
 
+  // WebUIBrowserTest:
+  void SetUpCommandLine(base::CommandLine* command_line) override;
+
  protected:
   // Sets the pref to allow or prohibit deleting history entries.
   void SetDeleteAllowed(bool allowed);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DownloadsUIBrowserTest);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_DOWNLOADS_UI_BROWSERTEST_H_