Revert of Run exo tests in parallel

components/exo/test/run_all_unittests.cc

Index: components/exo/test/run_all_unittests.cc
diff --git a/components/exo/test/run_all_unittests.cc b/components/exo/test/run_all_unittests.cc
index cc90b710dfee0df5e39484164dcbc5b39e385601..e69d387c9b75cf2b0ecbc2e29066570ec7e73a87 100644
--- a/components/exo/test/run_all_unittests.cc
+++ b/components/exo/test/run_all_unittests.cc
@@ -9,7 +9,7 @@
 int main(int argc, char** argv) {
   ash::test::AuraShellTestSuite test_suite(argc, argv);
 
-  return base::LaunchUnitTests(argc, argv,
-                               base::Bind(&ash::test::AuraShellTestSuite::Run,
-                                          base::Unretained(&test_suite)));
+  return base::LaunchUnitTestsSerially(
+      argc, argv, base::Bind(&ash::test::AuraShellTestSuite::Run,
+                             base::Unretained(&test_suite)));
 }