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 e098cef2d76d73d441e976b5cfaf5b3b2b8b29b0..33f4160888e5f9877fddc237fde1d8fc2bf17544 100644
--- a/ios/crnet/crnet_environment.mm
+++ b/ios/crnet/crnet_environment.mm
@@ -139,13 +139,13 @@ 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