base: Mark MessageLoop::Post*Task API deprecated

This is the first step in removing the direct MessageLoop task posting
API in favor of task_runner() and the TaskRunner APIs. See the design
doc for details[1].

BUG=465354

[1] https://docs.google.com/a/chromium.org/document/d/1qxdh2I61_aB_Uzh1QgNqvdWFBCL_E65G2smoSySw7KU/edit#heading=h.eqrpa9q6bsq5

Review URL: https://codereview.chromium.org/1013813003

Cr-Commit-Position: refs/heads/master@{#321674}


CrOS-Libchrome-Original-Commit: c8c18e9f1d3ac1033f9ca308143fc3b545475ebe
diff --git a/base/message_loop/message_loop.cc b/base/message_loop/message_loop.cc
index daa7782..eb0f968 100644
--- a/base/message_loop/message_loop.cc
+++ b/base/message_loop/message_loop.cc
@@ -275,31 +275,27 @@
 void MessageLoop::PostTask(
     const tracked_objects::Location& from_here,
     const Closure& task) {
-  DCHECK(!task.is_null()) << from_here.ToString();
-  incoming_task_queue_->AddToIncomingQueue(from_here, task, TimeDelta(), true);
+  message_loop_proxy_->PostTask(from_here, task);
 }
 
 void MessageLoop::PostDelayedTask(
     const tracked_objects::Location& from_here,
     const Closure& task,
     TimeDelta delay) {
-  DCHECK(!task.is_null()) << from_here.ToString();
-  incoming_task_queue_->AddToIncomingQueue(from_here, task, delay, true);
+  message_loop_proxy_->PostDelayedTask(from_here, task, delay);
 }
 
 void MessageLoop::PostNonNestableTask(
     const tracked_objects::Location& from_here,
     const Closure& task) {
-  DCHECK(!task.is_null()) << from_here.ToString();
-  incoming_task_queue_->AddToIncomingQueue(from_here, task, TimeDelta(), false);
+  message_loop_proxy_->PostNonNestableTask(from_here, task);
 }
 
 void MessageLoop::PostNonNestableDelayedTask(
     const tracked_objects::Location& from_here,
     const Closure& task,
     TimeDelta delay) {
-  DCHECK(!task.is_null()) << from_here.ToString();
-  incoming_task_queue_->AddToIncomingQueue(from_here, task, delay, false);
+  message_loop_proxy_->PostNonNestableDelayedTask(from_here, task, delay);
 }
 
 void MessageLoop::Run() {