Reland 66791 (change was innocent)...

base/singleton.h

Index: base/singleton.h
===================================================================
--- base/singleton.h	(revision 66806)
+++ base/singleton.h	(working copy)
@@ -9,6 +9,7 @@
 #include "base/at_exit.h"
 #include "base/atomicops.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
+#include "base/thread_restrictions.h"
 
 // Default traits for Singleton<Type>. Calls operator new and operator delete on
 // the object. Registers automatic deletion at process exit.
@@ -30,6 +31,11 @@
   // Set to true to automatically register deletion of the object on process
   // exit. See below for the required call that makes this happen.
   static const bool kRegisterAtExit = true;
+
+  // Set to false to disallow access on a non-joinable thread.  This is
+  // different from kRegisterAtExit because StaticMemorySingletonTraits allows
+  // access on non-joinable threads, and gracefully handles this.
+  static const bool kAllowedToAccessOnNonjoinableThread = false;
 };
 
 
@@ -39,6 +45,7 @@
 template<typename Type>
 struct LeakySingletonTraits : public DefaultSingletonTraits<Type> {
   static const bool kRegisterAtExit = false;
+  static const bool kAllowedToAccessOnNonjoinableThread = true;
 };
 
 
@@ -85,6 +92,7 @@
   }
 
   static const bool kRegisterAtExit = true;
+  static const bool kAllowedToAccessOnNonjoinableThread = true;
 
   // Exposed for unittesting.
   static void Resurrect() {
@@ -176,6 +184,9 @@
 
   // Return a pointer to the one true instance of the class.
   static Type* get() {
+    if (!Traits::kAllowedToAccessOnNonjoinableThread)
+      base::ThreadRestrictions::AssertSingletonAllowed();
+
     // Our AtomicWord doubles as a spinlock, where a value of
     // kBeingCreatedMarker means the spinlock is being held for creation.
     static const base::subtle::AtomicWord kBeingCreatedMarker = 1;