Fix base::internal::Singleton to use acquire loads instead of nobarrier ones.

base/memory/singleton.cc

Index: base/memory/singleton.cc
===================================================================
--- base/memory/singleton.cc	(revision 255285)
+++ base/memory/singleton.cc	(working copy)
@@ -18,7 +18,10 @@
   // the object has been created.
   subtle::AtomicWord value;
   while (true) {
-    value = subtle::NoBarrier_Load(instance);
+    // The load has acquire memory ordering as the thread which reads the
+    // instance pointer must acquire visibility over the associated data.
+    // The pairing Release_Store operation is in Singleton::get().
+    value = subtle::Acquire_Load(instance);
     if (value != kBeingCreatedMarker)
       break;
     PlatformThread::YieldCurrentThread();