Remove content::BrowserThread::PostAfterStartupTask

It is no longer used, and you should be posting tasks with BEST_EFFORT
priority instead.

Bug: 887407
Change-Id: I3792d648a5a9702ccdf08859b7bf65b58c5dbafe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1645215
Auto-Submit: Carlos Caballero <carlscab@google.com>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666241}

content/browser/browser_thread_impl.cc

@@ -162,15 +162,6 @@ const char* BrowserThreadImpl::GetThreadName(BrowserThread::ID thread) {
   return "Unknown Thread";
 }
 
-// static
-void BrowserThread::PostAfterStartupTask(
-    const base::Location& from_here,
-    const scoped_refptr<base::TaskRunner>& task_runner,
-    base::OnceClosure task) {
-  GetContentClient()->browser()->PostAfterStartupTask(from_here, task_runner,
-                                                      std::move(task));
-}
-
 // static
 bool BrowserThread::IsThreadInitialized(ID identifier) {
   DCHECK_GE(identifier, 0);

content/public/browser/browser_thread.h

@@ -93,29 +93,6 @@ class CONTENT_EXPORT BrowserThread {
         ->ReleaseSoon(from_here, std::move(object));
   }
 
-  // For use with scheduling non-critical tasks for execution after startup.
-  // The order or execution of tasks posted here is unspecified even when
-  // posting to a SequencedTaskRunner and tasks are not guaranteed to be run
-  // prior to browser shutdown.
-  // When called after the browser startup is complete, will post |task|
-  // to |task_runner| immediately.
-  // Note: see related ContentBrowserClient::PostAfterStartupTask.
-  //
-  // TODO(crbug.com/887407): Replace callsites with PostTaskWithTraits and
-  // appropriate traits (TBD).
-  //
-  // DEPRECATED(carlscab): This method is deprecated and will go away soon,
-  // consider posting the task with priority BEST_EFFORT. For example:
-  // base::PostTaskWithTraits(
-  //   FROM_HERE, {content::BrowserThread::UI, base::TaskPriority::BEST_EFFORT},
-  //   base::BindOnce(...));
-  // Or if you need to run in a special TaskRunner by using the
-  // PostBestEffortTask function below
-  static void PostAfterStartupTask(
-      const base::Location& from_here,
-      const scoped_refptr<base::TaskRunner>& task_runner,
-      base::OnceClosure task);
-
   // Posts a |task| to run at BEST_EFFORT priority using an arbitrary
   // |task_runner| for which we do not control the priority
   //