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 b652408781292dcabc393cb8919471f25ea4acb3..46c25d64699176f9ace8a1e48301213009acf726 100644
--- a/content/browser/browser_main_loop.cc
+++ b/content/browser/browser_main_loop.cc
@@ -31,6 +31,7 @@
 #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"
@@ -741,6 +742,14 @@ int BrowserMainLoop::PreCreateThreads() {
     result_code_ = parts_->PreCreateThreads();
   }
 
+  // Enable SequencedWorkerPool for this process. If the
+  // BrowserMainParts::PreCreateThreads() call above has already enabled
+  // SequencedWorkerPool (with or without redirection to TaskScheduler), this
+  // has no effect.
+  // TODO(fdoray): Remove this once the SequencedWorkerPool to TaskScheduler
+  // redirection experiment concludes https://crbug.com/622400.
+  base::SequencedWorkerPool::EnableForProcess();
+
   const base::CommandLine* command_line =
       base::CommandLine::ForCurrentProcess();
   // Note that we do not initialize a new FeatureList when calling this for