Revert of Reland: Lazily initialize MessageLoop for faster thread startup

base/threading/thread_unittest.cc

Index: base/threading/thread_unittest.cc
diff --git a/base/threading/thread_unittest.cc b/base/threading/thread_unittest.cc
index e86c7582e319969116be31da9437dca975c30dba..a89768e9d0a2690e97f6f1dc786ed097450d69d2 100644
--- a/base/threading/thread_unittest.cc
+++ b/base/threading/thread_unittest.cc
@@ -194,12 +194,11 @@
   EXPECT_EQ("ThreadName", a.thread_name());
 }
 
-// Make sure Init() is called after Start() and before
-// WaitUntilThreadInitialized() returns.
+// Make sure we can't use a thread between Start() and Init().
 TEST_F(ThreadTest, SleepInsideInit) {
   SleepInsideInitThread t;
   EXPECT_FALSE(t.InitCalled());
-  t.StartAndWaitForTesting();
+  t.Start();
   EXPECT_TRUE(t.InitCalled());
 }