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

base/lazy_instance.h

Index: base/lazy_instance.h
===================================================================
--- base/lazy_instance.h	(revision 66790)
+++ base/lazy_instance.h	(working copy)
@@ -36,19 +36,14 @@
 #define BASE_LAZY_INSTANCE_H_
 #pragma once
 
-#include <new>  // For placement new.
-
 #include "base/atomicops.h"
 #include "base/basictypes.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
-#include "base/thread_restrictions.h"
 
 namespace base {
 
 template <typename Type>
 struct DefaultLazyInstanceTraits {
-  static const bool kAllowedToAccessOnNonjoinableThread = false;
-
   static Type* New(void* instance) {
     // Use placement new to initialize our instance in our preallocated space.
     // The parenthesis is very important here to force POD type initialization.
@@ -62,8 +57,6 @@
 
 template <typename Type>
 struct LeakyLazyInstanceTraits {
-  static const bool kAllowedToAccessOnNonjoinableThread = true;
-
   static Type* New(void* instance) {
     return DefaultLazyInstanceTraits<Type>::New(instance);
   }
@@ -119,9 +112,6 @@
   }
 
   Type* Pointer() {
-    if (!Traits::kAllowedToAccessOnNonjoinableThread)
-      base::ThreadRestrictions::AssertSingletonAllowed();
-
     // We will hopefully have fast access when the instance is already created.
     if ((base::subtle::NoBarrier_Load(&state_) != STATE_CREATED) &&
         NeedsInstance()) {
@@ -136,6 +126,7 @@
     // and CompleteInstance(...) happens before "return instance_" below.
     // See the corresponding HAPPENS_BEFORE in CompleteInstance(...).
     ANNOTATE_HAPPENS_AFTER(&state_);
+
     return instance_;
   }