Cleanup PreferenceMACs on browser_tests startup

content/public/test/test_launcher.h

Index: content/public/test/test_launcher.h
diff --git a/content/public/test/test_launcher.h b/content/public/test/test_launcher.h
index b58f9b75d78973ff3c38e424d1a1eac5dcca5675..82079942efcbe1a7c2d5e57f2634c031873e299d 100644
--- a/content/public/test/test_launcher.h
+++ b/content/public/test/test_launcher.h
@@ -58,6 +58,11 @@ class TestLauncherDelegate {
       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) {}