Cleanup PreferenceMACs on browser_tests startup

chrome/test/base/chrome_test_launcher.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_TEST_BASE_CHROME_TEST_LAUNCHER_H_
 #define CHROME_TEST_BASE_CHROME_TEST_LAUNCHER_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 18 matching lines @@
   explicit ChromeTestLauncherDelegate(ChromeTestSuiteRunner* runner);
   ~ChromeTestLauncherDelegate() override;
 
  protected:
   // content::TestLauncherDelegate:
   int RunTestSuite(int argc, char** argv) override;
   bool AdjustChildProcessCommandLine(
       base::CommandLine* command_line,
       const base::FilePath& temp_data_dir) override;
   content::ContentMainDelegate* CreateContentMainDelegate() override;
+  void PreSharding() override;
 
  private:
   ChromeTestSuiteRunner* runner_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeTestLauncherDelegate);
 };
 
 // Launches Chrome browser tests. |default_jobs| is number of test jobs to be
 // run in parallel, unless overridden from the command line. Returns exit code.
 // Does not take ownership of ChromeTestLauncherDelegate.
 int LaunchChromeTests(int default_jobs,
                       content::TestLauncherDelegate* delegate,
                       int argc,
                       char** argv);
 
 #endif  // CHROME_TEST_BASE_CHROME_TEST_LAUNCHER_H_