Issue #4826 - Use latch to replace thread-sleeping in tests

test/Prefs.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 133 matching lines @@
 TEST_F(PrefsTest, PrefsPersist)
 {
   ASSERT_EQ("patterns.ini", filterEngine->GetPref("patternsfile")->AsString());
   ASSERT_EQ(24, filterEngine->GetPref("patternsbackupinterval")->AsInt());
   ASSERT_TRUE(filterEngine->GetPref("subscriptions_autoupdate")->AsBool());
 
   filterEngine->SetPref("patternsfile", jsEngine->NewValue("filters.ini"));
   filterEngine->SetPref("patternsbackupinterval", jsEngine->NewValue(48));
   filterEngine->SetPref("subscriptions_autoupdate", jsEngine->NewValue(false));
 
-  std::this_thread::sleep_for(std::chrono::milliseconds(100));
+  std::this_thread::sleep_for(std::chrono::milliseconds(100)); // RACE
 
   ASSERT_FALSE(fileSystem->prefsContents.empty());
 
   Reset();
 
   ASSERT_EQ("filters.ini", filterEngine->GetPref("patternsfile")->AsString());
   ASSERT_EQ(48, filterEngine->GetPref("patternsbackupinterval")->AsInt());
   ASSERT_FALSE(filterEngine->GetPref("subscriptions_autoupdate")->AsBool());
 }
 
@@ skipping 50 matching lines @@
 TEST_F(PrefsTest, PrefsPersistWhenPreconfigured)
 {
   boolPrefsInitializer preconfiguredPrefs;
   preconfiguredPrefs["suppress_first_run_page"] = true;
   Reset(preconfiguredPrefs);
 
   ASSERT_TRUE(filterEngine->GetPref("suppress_first_run_page")->IsBool());
   ASSERT_TRUE(filterEngine->GetPref("suppress_first_run_page")->AsBool());
   filterEngine->SetPref("suppress_first_run_page", jsEngine->NewValue(false));
 
-  std::this_thread::sleep_for(std::chrono::milliseconds(100));
+  std::this_thread::sleep_for(std::chrono::milliseconds(100)); // RACE
 
   ASSERT_FALSE(fileSystem->prefsContents.empty());
 
   Reset(preconfiguredPrefs);
 
   ASSERT_TRUE(filterEngine->GetPref("suppress_first_run_page")->IsBool());
   ASSERT_FALSE(filterEngine->GetPref("suppress_first_run_page")->AsBool());
 }