Remove all remaining traces of MessageLoopProxy.

net/url_request/url_request_context_getter.cc

Index: net/url_request/url_request_context_getter.cc
diff --git a/net/url_request/url_request_context_getter.cc b/net/url_request/url_request_context_getter.cc
index 1808617521439b9577c6cf5cd74f7708dc3b90d5..022aa0f958c3c9f7fe520101996c0d8194915444 100644
--- a/net/url_request/url_request_context_getter.cc
+++ b/net/url_request/url_request_context_getter.cc
@@ -47,7 +47,7 @@ void URLRequestContextGetter::OnDestruct() const {
       }
     }
   }
-  // If no IO message loop proxy was available, we will just leak memory.
+  // If no IO task runner was available, we will just leak memory.
   // This is also true if the IO thread is gone.
 }