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 856a67b6183c1ec3e50e6574c4e3cab85f61944a..8f82a58652ba63735138e98b1fed28326e2143e6 100644
--- a/content/browser/browser_main_loop.h
+++ b/content/browser/browser_main_loop.h
@@ -26,10 +26,10 @@ namespace base {
 class CommandLine;
 class FilePath;
 class HighResolutionTimerManager;
+class MemoryPressureMonitor;
 class MessageLoop;
 class PowerMonitor;
 class SystemMonitor;
-class MemoryPressureMonitor;
 namespace trace_event {
 class TraceEventSystemStatsMonitor;
 }  // namespace trace_event
@@ -273,6 +273,9 @@ class CONTENT_EXPORT BrowserMainLoop {
 #endif
 
   // Members initialized in |CreateThreads()| ----------------------------------
+  // Note: some |*_thread_| members below may never be initialized when
+  // redirection to TaskScheduler is enabled. (ref.
+  // ContentBrowserClient::RedirectNonUINonIOBrowserThreadsToTaskScheduler()).
   std::unique_ptr<BrowserProcessSubThread> db_thread_;
   std::unique_ptr<BrowserProcessSubThread> file_user_blocking_thread_;
   std::unique_ptr<BrowserProcessSubThread> file_thread_;