Improve support for multiselect list box accessibility on Windows.

base/atomic_ref_count.h

Index: base/atomic_ref_count.h
===================================================================
--- base/atomic_ref_count.h	(revision 111700)
+++ base/atomic_ref_count.h	(working copy)
@@ -51,6 +51,24 @@
   return base::AtomicRefCountDecN(ptr, 1);
 }
 
+// Increment a reference count by 1 and return the new value.
+inline AtomicRefCount AtomicRefCountIncAndReturnValue(
+    volatile AtomicRefCount *ptr) {
+  ANNOTATE_HAPPENS_BEFORE(ptr);
+  AtomicRefCount res = subtle::Barrier_AtomicIncrement(ptr, 1);
+  ANNOTATE_HAPPENS_AFTER(ptr);
+  return res;
+}
+
+// Decrement a reference count by 1 and return the new value.
+inline AtomicRefCount AtomicRefCountDecAndReturnValue(
+    volatile AtomicRefCount *ptr) {
+  ANNOTATE_HAPPENS_BEFORE(ptr);
+  AtomicRefCount res = subtle::Barrier_AtomicIncrement(ptr, -1);
+  ANNOTATE_HAPPENS_AFTER(ptr);
+  return res;
+}
+
 // Return whether the reference count is one.  If the reference count is used
 // in the conventional way, a refrerence count of 1 implies that the current
 // thread owns the reference and no other thread shares it.  This call performs