Experiment with redirecting all BrowserThreads (but UI/IO) to TaskScheduler

content/browser/browser_main_loop.h

Index: content/browser/browser_main_loop.h
diff --git a/content/browser/browser_main_loop.h b/content/browser/browser_main_loop.h
index 1464de7ced9cb6ae38c160ead17e1a935d9a6474..fdde0f4f141592f9abd7947f6b5efa3dd2a08719 100644
--- a/content/browser/browser_main_loop.h
+++ b/content/browser/browser_main_loop.h
@@ -26,10 +26,11 @@ namespace base {
 class CommandLine;
 class FilePath;
 class HighResolutionTimerManager;
+class MemoryPressureMonitor;
 class MessageLoop;
 class PowerMonitor;
+class SingleThreadTaskRunner;
 class SystemMonitor;
-class MemoryPressureMonitor;
 namespace trace_event {
 class TraceEventSystemStatsMonitor;
 }  // namespace trace_event
@@ -277,6 +278,12 @@ class CONTENT_EXPORT BrowserMainLoop {
   std::unique_ptr<BrowserProcessSubThread> file_thread_;
   std::unique_ptr<BrowserProcessSubThread> process_launcher_thread_;
   std::unique_ptr<BrowserProcessSubThread> cache_thread_;
+  scoped_refptr<base::SingleThreadTaskRunner> db_task_runner_;
+  scoped_refptr<base::SingleThreadTaskRunner> file_user_blocking_task_runner_;
+  scoped_refptr<base::SingleThreadTaskRunner> file_task_runner_;
+  scoped_refptr<base::SingleThreadTaskRunner> process_launcher_task_runner_;
+  scoped_refptr<base::SingleThreadTaskRunner> cache_task_runner_;
+  // The IO thread is never redirected to TaskScheduler at this point.
   std::unique_ptr<BrowserProcessSubThread> io_thread_;
 
   // Members initialized in |BrowserThreadsStarted()| --------------------------