Make DisplayLinkMac RefCountedThreadSafe

ui/accelerated_widget_mac/display_link_mac.h

Index: ui/accelerated_widget_mac/display_link_mac.h
diff --git a/ui/accelerated_widget_mac/display_link_mac.h b/ui/accelerated_widget_mac/display_link_mac.h
index f9269e1e374fffe76f862a3a4b86471200f9eb9f..c376c702a73bc1511b295987eb086ad795ba16c6 100644
--- a/ui/accelerated_widget_mac/display_link_mac.h
+++ b/ui/accelerated_widget_mac/display_link_mac.h
@@ -22,8 +22,8 @@ class SingleThreadTaskRunner;
 
 namespace ui {
 
-class ACCELERATED_WIDGET_MAC_EXPORT DisplayLinkMac :
-    public base::RefCounted<DisplayLinkMac> {
+class ACCELERATED_WIDGET_MAC_EXPORT DisplayLinkMac
+    : public base::RefCountedThreadSafe<DisplayLinkMac> {
  public:
   static scoped_refptr<DisplayLinkMac> GetForDisplay(
       CGDirectDisplayID display_id);
@@ -41,7 +41,7 @@ class ACCELERATED_WIDGET_MAC_EXPORT DisplayLinkMac :
   void NotifyCurrentTime(const base::TimeTicks& now);
 
  private:
-  friend class base::RefCounted<DisplayLinkMac>;
+  friend class base::RefCountedThreadSafe<DisplayLinkMac>;
 
   DisplayLinkMac(
       CGDirectDisplayID display_id,