Add ability to return moved value from FunctorMessageHandler, Optional.

webrtc/base/thread.h

Index: webrtc/base/thread.h
diff --git a/webrtc/base/thread.h b/webrtc/base/thread.h
index 29b78e18452a28b59f844bcc81432949ee358e4e..f74222657ebfce2874b75d709f597b0341ced32b 100644
--- a/webrtc/base/thread.h
+++ b/webrtc/base/thread.h
@@ -168,7 +168,7 @@ class LOCKABLE Thread : public MessageQueue {
   ReturnT Invoke(const Location& posted_from, const FunctorT& functor) {
     FunctorMessageHandler<ReturnT, FunctorT> handler(functor);
     InvokeInternal(posted_from, &handler);
-    return handler.result();
+    return handler.ConsumeResult();
   }
 
   // From MessageQueue