Update from https://crrev.com/328418

base/message_loop/message_loop_proxy.h

Index: base/message_loop/message_loop_proxy.h
diff --git a/base/message_loop/message_loop_proxy.h b/base/message_loop/message_loop_proxy.h
index 88eeac4ee6d50a55ffefaa560864c59d1241b9f8..d5ecc041b6fc4a3b34c382cc9c2826739fa017aa 100644
--- a/base/message_loop/message_loop_proxy.h
+++ b/base/message_loop/message_loop_proxy.h
@@ -10,6 +10,18 @@
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 
+// MessageLoopProxy is deprecated. Code should prefer to depend on TaskRunner
+// (or the various specializations) for passing task runners around, and should
+// use ThreadTaskRunnerHandle::Get() to get the thread's associated task runner.
+//
+// See http://crbug.com/391045 for more details.
+// Example for these changes:
+//
+// base::MessageLoopProxy::current() -> base::ThreadTaskRunnerHandle::Get()
+// scoped_refptr<base::MessageLoopProxy> ->
+//     scoped_refptr<base::SingleThreadTaskRunner>
+// base::MessageLoopProxy -> base::SingleThreadTaskRunner
+
 namespace base {
 
 // This class provides a thread-safe refcounted interface to the Post* methods