Revert 66719 - Reland r65996. Disallows Singletons on non-joinable thread....

chrome/browser/browser_thread.cc

Index: chrome/browser/browser_thread.cc
===================================================================
--- chrome/browser/browser_thread.cc	(revision 66790)
+++ chrome/browser/browser_thread.cc	(working copy)
@@ -6,7 +6,6 @@
 
 #include "base/message_loop.h"
 #include "base/message_loop_proxy.h"
-#include "base/thread_restrictions.h"
 
 // Friendly names for the well-known threads.
 static const char* browser_thread_names[BrowserThread::ID_COUNT] = {
@@ -113,11 +112,6 @@
 
 // static
 bool BrowserThread::CurrentlyOn(ID identifier) {
-  // We shouldn't use MessageLoop::current() since it uses LazyInstance which
-  // may be deleted by ~AtExitManager when a WorkerPool thread calls this
-  // function.
-  // http://crbug.com/63678
-  base::ThreadRestrictions::ScopedAllowSingleton allow_singleton;
   AutoLock lock(lock_);
   DCHECK(identifier >= 0 && identifier < ID_COUNT);
   return browser_threads_[identifier] &&
@@ -166,11 +160,6 @@
 
 // static
 bool BrowserThread::GetCurrentThreadIdentifier(ID* identifier) {
-  // We shouldn't use MessageLoop::current() since it uses LazyInstance which
-  // may be deleted by ~AtExitManager when a WorkerPool thread calls this
-  // function.
-  // http://crbug.com/63678
-  base::ThreadRestrictions::ScopedAllowSingleton allow_singleton;
   MessageLoop* cur_message_loop = MessageLoop::current();
   for (int i = 0; i < ID_COUNT; ++i) {
     if (browser_threads_[i] &&