base::RefCounted now DCHECKs when referenced from multiple threads.

ipc/ipc_message_attachment.h

Index: ipc/ipc_message_attachment.h
diff --git a/ipc/ipc_message_attachment.h b/ipc/ipc_message_attachment.h
index ba7f0e83f90567407ce69f59cd891b10492f1cbc..a88a589367fc1a9058faac9ed8846cc2e37d4433 100644
--- a/ipc/ipc_message_attachment.h
+++ b/ipc/ipc_message_attachment.h
@@ -14,8 +14,9 @@ namespace IPC {
 
 // Auxiliary data sent with |Message|. This can be a platform file descriptor
 // or a mojo |MessagePipe|. |GetType()| returns the type of the subclass.
+// TODO(mgiuca): Avoid using UnsafeRefCounted. http://crbug.com/469952.
 class IPC_EXPORT MessageAttachment
-    : public base::RefCounted<MessageAttachment> {
+    : public base::UnsafeRefCounted<MessageAttachment> {
  public:
   enum Type {
     TYPE_PLATFORM_FILE,  // The instance is |PlatformFileAttachment|.
@@ -29,7 +30,7 @@ class IPC_EXPORT MessageAttachment
 #endif  // OS_POSIX
 
  protected:
-  friend class base::RefCounted<MessageAttachment>;
+  friend class base::UnsafeRefCounted<MessageAttachment>;
   MessageAttachment();
   virtual ~MessageAttachment();