Remove remaining calls to deprecated MessageLoop methods on Mac.

ios/crnet/crnet_environment.mm

Index: ios/crnet/crnet_environment.mm
diff --git a/ios/crnet/crnet_environment.mm b/ios/crnet/crnet_environment.mm
index c4daef807b4b72512fc0de55ca3c61004800dc4b..024fc5fc4f741e078da45e37ff30443c0e53c050 100644
--- a/ios/crnet/crnet_environment.mm
+++ b/ios/crnet/crnet_environment.mm
@@ -137,13 +137,13 @@ class CrNetHttpProtocolHandlerDelegate
 void CrNetEnvironment::PostToNetworkThread(
     const tracked_objects::Location& from_here,
     const base::Closure& task) {
-  network_io_thread_->message_loop()->PostTask(from_here, task);
+  network_io_thread_->task_runner()->PostTask(from_here, task);
 }
 
 void CrNetEnvironment::PostToFileUserBlockingThread(
     const tracked_objects::Location& from_here,
     const base::Closure& task) {
-  file_user_blocking_thread_->message_loop()->PostTask(from_here, task);
+  file_user_blocking_thread_->task_runner()->PostTask(from_here, task);
 }
 
 // static