Prevent a thread startup race in ScheduleWorkTest which causes a nullptr dereference of a message p…

base/message_loop/message_pump_perftest.cc

Index: base/message_loop/message_pump_perftest.cc
diff --git a/base/message_loop/message_pump_perftest.cc b/base/message_loop/message_pump_perftest.cc
index 7d833befa6158a33b5e64810a928c85abf547798..9f76064ce38e4c586dcb0db1fd5bd1b406ec5da7 100644
--- a/base/message_loop/message_pump_perftest.cc
+++ b/base/message_loop/message_pump_perftest.cc
@@ -70,6 +70,13 @@ class ScheduleWorkTest : public testing::Test {
     {
       target_.reset(new Thread("target"));
       target_->StartWithOptions(Thread::Options(target_type, 0u));
+
+      // Without this, it's possible for the scheduling threads to start and run
+      // before the target thread. In this case, the scheduling threads will
+      // call target_message_loop()->ScheduleWork(), which dereferences the
+      // loop's message pump, which is only created after the target thread has
+      // finished starting.
+      target_->WaitUntilThreadStarted();
     }
 
     ScopedVector<Thread> scheduling_threads;