Made MessagePump a non-thread safe class.

net/dns/serial_worker_unittest.cc

Index: net/dns/serial_worker_unittest.cc
diff --git a/net/dns/serial_worker_unittest.cc b/net/dns/serial_worker_unittest.cc
index 70259f72800db9ebff905fc446281bb41ff5d4ef..442526f29d21a3de66ff15d7af5cabbe7c5ad02f 100644
--- a/net/dns/serial_worker_unittest.cc
+++ b/net/dns/serial_worker_unittest.cc
@@ -141,7 +141,7 @@ TEST_F(SerialWorkerTest, ExecuteAndSerializeReads) {
     WaitForWork();
     RunUntilBreak("OnWorkFinished");
 
-    message_loop_->AssertIdle();
+    EXPECT_TRUE(message_loop_->IsIdleForTesting());
   }
 
   // Schedule two calls. OnWork checks if it is called serially.
@@ -154,7 +154,7 @@ TEST_F(SerialWorkerTest, ExecuteAndSerializeReads) {
   RunUntilBreak("OnWorkFinished");
 
   // No more tasks should remain.
-  message_loop_->AssertIdle();
+  EXPECT_TRUE(message_loop_->IsIdleForTesting());
 }
 
 }  // namespace