Revert of Add thread checking to RunLoop, deprecate MessageLoopRunner.

base/run_loop.h

Index: base/run_loop.h
diff --git a/base/run_loop.h b/base/run_loop.h
index 077d097ba9a2a35c6ec51d017f588b9f195e48c0..635018f434ec1a69c331366d80506ab2dc6a2ce0 100644
--- a/base/run_loop.h
+++ b/base/run_loop.h
@@ -10,7 +10,6 @@
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop.h"
-#include "base/threading/thread_checker.h"
 #include "build/build_config.h"
 
 namespace base {
@@ -106,8 +105,6 @@
   // that we should quit Run once it becomes idle.
   bool quit_when_idle_received_;
 
-  base::ThreadChecker thread_checker_;
-
   // WeakPtrFactory for QuitClosure safety.
   base::WeakPtrFactory<RunLoop> weak_factory_;