Revert of Disallow posting tasks to SequencedWorkerPools by default.

content/browser/browser_main_loop.cc

Index: content/browser/browser_main_loop.cc
diff --git a/content/browser/browser_main_loop.cc b/content/browser/browser_main_loop.cc
index c87ed7b42d65bcc9b5232a9551886a98d26100d4..648873d6c243ff38638dfb43e33d088dd150381f 100644
--- a/content/browser/browser_main_loop.cc
+++ b/content/browser/browser_main_loop.cc
@@ -31,7 +31,6 @@
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "base/system_monitor/system_monitor.h"
-#include "base/threading/sequenced_worker_pool.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/timer/hi_res_timer_manager.h"
@@ -736,24 +735,12 @@
 }
 
 int BrowserMainLoop::PreCreateThreads() {
-  // SequencedWorkerPool shouldn't be enabled yet. It should be enabled below by
-  // either |parts_|->PreCreateThreads() or
-  // base::SequencedWorkerPool::EnableForProcess().
-  DCHECK(!base::SequencedWorkerPool::IsEnabled());
-
   if (parts_) {
     TRACE_EVENT0("startup",
         "BrowserMainLoop::CreateThreads:PreCreateThreads");
 
     result_code_ = parts_->PreCreateThreads();
   }
-
-  // Enable SequencedWorkerPool if |parts_|->PreCreateThreads() hasn't enabled
-  // it.
-  // TODO(fdoray): Remove this once the SequencedWorkerPool to TaskScheduler
-  // redirection experiment concludes https://crbug.com/622400.
-  if (!base::SequencedWorkerPool::IsEnabled())
-    base::SequencedWorkerPool::EnableForProcess();
 
   const base::CommandLine* command_line =
       base::CommandLine::ForCurrentProcess();