Cleanup PreferenceMACs on browser_tests startup

content/public/test/test_launcher.h

 // 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.
 
 #ifndef CONTENT_PUBLIC_TEST_TEST_LAUNCHER_H_
 #define CONTENT_PUBLIC_TEST_TEST_LAUNCHER_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 40 matching lines @@
   // Called prior to running each test. The delegate may alter the CommandLine
   // and options used to launch the subprocess. Additionally the client may
   // return a TestState that is destroyed once the test completes as well as
   // once the test process is launched.
   //
   // NOTE: this is not called if --single_process is supplied.
   virtual std::unique_ptr<TestState> PreRunTest(
       base::CommandLine* command_line,
       base::TestLauncher::LaunchOptions* test_launch_options);
 
+  // Allows a TestLauncherDelegate to cleanup any global state (e.g. registry)
+  // before sharding the tests into multiple processes who may access that
+  // state.
+  virtual void PreShardingCleanup() {}

[jam, 2017/05/17 19:06:16]

nit: just call it PreSharding and don't mention implementation details that
chrome uses like registry, cleanup etc

[gab, 2017/05/17 20:01:05]

Done.

+
   // Allows a TestLauncherDelegate to adjust the number of |default_jobs| used
   // when --test-launcher-jobs isn't specified on the command-line.
   virtual void AdjustDefaultParallelJobs(int* default_jobs) {}
 
   // Called prior to returning from LaunchTests(). Gives the delegate a chance
   // to do cleanup before state created by TestLauncher has been destroyed (such
   // as the AtExitManager).
   virtual void OnDoneRunningTests();
 
  protected:
   virtual ~TestLauncherDelegate();
 };
 
 // Launches tests using |launcher_delegate|. |default_jobs| is number
 // of test jobs to be run in parallel, unless overridden from the command line.
 // Returns exit code.
 int LaunchTests(TestLauncherDelegate* launcher_delegate,
                 int default_jobs,
                 int argc,
                 char** argv) WARN_UNUSED_RESULT;
 
 TestLauncherDelegate* GetCurrentTestLauncherDelegate();
 ContentMainParams* GetContentMainParams();
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_TEST_TEST_LAUNCHER_H_