Remove all remaining traces of MessageLoopProxy.

base/tracked_objects.h

Index: base/tracked_objects.h
diff --git a/base/tracked_objects.h b/base/tracked_objects.h
index 81962f3fe9a7298654b2dc1dc3c93fd3bef36e25..7ef0317c39bb1712873d9a78856b5c32220aa1fd 100644
--- a/base/tracked_objects.h
+++ b/base/tracked_objects.h
@@ -174,7 +174,7 @@ struct TrackingInfo;
 // (worker threads don't have message loops generally, and hence gathering from
 // them will continue to be asynchronous).  We had an implementation of this in
 // the past, but the difficulty is dealing with message loops being terminated.
-// We can *try* to spam the available threads via some message loop proxy to
+// We can *try* to spam the available threads via some task runner to
 // achieve this feat, and it *might* be valuable when we are collecting data
 // for upload via UMA (where correctness of data may be more significant than
 // for a single screen of about:profiler).