Give the post-and-reply worker pool test a chance to finish on iOS

base/threading/worker_pool_unittest.cc

Index: base/threading/worker_pool_unittest.cc
diff --git a/base/threading/worker_pool_unittest.cc b/base/threading/worker_pool_unittest.cc
index 10ca4f151183415371d86e91bcae266791848f36..5021b2f73304f25c9365af97005d67ce3361fcee 100644
--- a/base/threading/worker_pool_unittest.cc
+++ b/base/threading/worker_pool_unittest.cc
@@ -98,6 +98,11 @@ TEST_F(WorkerPoolTest, MAYBE_PostTaskAndReply) {
   const TimeDelta kMaxDuration = TestTimeouts::tiny_timeout();
   TimeTicks start = TimeTicks::Now();
   while (!tester->finished() && TimeTicks::Now() - start < kMaxDuration) {
+#if defined(OS_IOS)
+    // Ensure that the other thread has a chance to run even on a single-core
+    // device.
+    pthread_yield_np();
+#endif
     MessageLoop::current()->RunAllPending();
   }
   EXPECT_TRUE(tester->finished());